The better question is: If Charles Taze Russell was a free mason, why did he spend almost his entire life presenting a message that would oppose Freemasons' ideology?
The video speaks of Jehovah's Witnesses; Charles Taze Russell was never a member of the organization known as Jehovah's Witnesses, and he preached against such an organization.
Russell taught that any new revealed truth would not contradict former revealed truth. However, I would add that there has been no actual "revealed" truth since the first century, although, in a general way, one's understanding of truths already revealed may indeed be contradictory as he progresses in understanding. In other words, as one progresses in understanding of the revealed light, he may have assimilated some errors along the way, which would contradict the revealed light, and which errors have to be discarded if one is to appreciate the revealed light.
Thus, in 1904, when Russell realized that assumptions had been placed upon 1914 that the scriptures did not bear out, and he realized that the end of the Gentile Times would see the beginning, not the end, of the time of trouble, he discarded his former view that the time of trouble was to end in 1914 (a view he had adopted from Nelson Barbour).
Russell, however, in saying that he was ready to modify his creed according to "increase of light" did not speak as "central authority" of an organization such as the Jehovah's Witnesses. In saying "increase of light", it could only be applied as meaning increase of understanding of the light as revealed in the Bible. Any increase of understanding of light cannot contradict what has already been revealed.
The video is correct that Russell did not claim infallibility; he, in fact, disclaimed such. He openly admitted the possibility that he could be in error; and openly stated that he was not a prophet, but rather a fallible student of Bible prophecy. He disclaimed that his expectations were prophecy.
Isaiah 29:18 WEB
In that day shall the deaf hear the words of the book, and the eyes of the blind shall see out of obscurity and out of darkness.
This "day" feature of the englightenment of the world has not yet arrived, except as reckoned to the new creature in Christ, for whom all things are new. (2 Corinthians 5:17) The new creature, the son of God, is not of this world that has been condemned in Adam, but is reckoned as having tasted of the powers of the age to come. (John 15:19; 17:14; Hebrews 6:5) Thus, the new creature, the son of God, in this age, actually belongs to that "day" which is yet to come. (Romans 13:12,13; Ephesians 4:30; 1 Thessalonians 5:5-9) The enlightenment of the world cannot come until after Satan is abyssed, so that he will no longer be able to deceive the heathen. (Revelation 20:1-4)The Scriptures tell us that darkness now covers the earth, society, and gross darkness the people. Yet in God’s due time the light of Truth will mount up high in the heavens as the Sun of Righteousness. It will scatter the darkness and clouds of sin and superstition. Thus from two standpoints a blessing will come by restraining the powers of darkness and by setting free the powers of light. Of that time we are further assured that the knowledge of Jehovah will fill the whole earth as the waters cover the sea. — Isaiah 60:2; Malachi 4:2; Isaiah 11:9.
The message of the good news that Russell referred to, however, is not the bad tidings of the great woe that will be for most of the people that they may be eternally destroyed in Armageddon (if they do not join the outward organization known as Jehovah's Witnesses) that Rutherford preached and that the JWs preach. The JWs are NOT preaching the Good News of great joy that shall be for all the people that Russell spoke of.
Although Rutherford began to reject portions of Good News as early as 1923, in 1938, Rutherford officially rejected the "good news of great joy that will for all the people" that Russell spoke of and replaced it with a new Gospel, which is not really a Gospel (Good News), but rather bad tidings of great woe that will be more most of the people that they are to be eternally destroyed for not accepting Rutherford's outward organization (kingdom).
Most of the JWs I have known have proven to me that they will indeed blindly follow whatever the men at the WT headquarters may say. Although some of them have admitted to me privately that they disagreed with some of things taught by the Society, publicly they will defend the organization even to point of dying for the outward organization, which, in effect, means closing their eyes to the facts and thus blindly following and even dying for the stand taken by those in the leadership positions in the org. Having once been associated with that org, I have seen this first-hand. Indeed, any open disagreement, and often even a private disclosure of disagreement, with "the Society" would call for a the person in disagreement to appear before a "judicial committee". Thus, there is an atempt at control through fear of men that does exist amongst the JWs.
The biggest "error" in connection with the cross would simply be that many use the cross for idolatrous purposes. One could argue against the use of the cross because of that association, but it is highly debatable that use of the cross itself is error.
While Russell did make some errors related to the measurement of the descending passageway of the Great Pyramid, the study of God's Witness in Egypt in itself is not error. Russell never wrote of "pyramidology" as such; that word as it is often used today could lead one to a misundersanding of the teaching that the Great Pyramid is God's witness in Egypt.
While Russell never seemed to fully appreciate the principle of idolatry as related to certain Christmas practices, he was correct in not assuming authority so as dictate to others what they should or should not do as related to celebrating any day.
The "Chart of the Ages" is not about "pyramidology", especially as that term is often used today. The pyramids used are similar to any organizational chart; the pyramids simply depict the development of God's Kingdom to its completion with Jesus as the top stone. Many corporations use similar "pyramids" to demonstrate their organizational structure.
Isaiah 29:24 WEB
They also who err in spirit shall come to understanding, and those who murmur shall receive instruction.
Isaiah 29:24 is another prophecy that cannot be fully fulfilled until after Satan is abyssed. (Revelation 20:1-4) Only after Satan is removed will the all those who are now erring and who now mumur be able to receive instruction in truth. Today, the world is still blinded by Satan's deceptions.
Nevertheless, the scripture does have a fulfillment in those who become New Creatures in Christ, in proportion as the new creature submits to the revealing and understanding of truth as found in the Bible that is available to him through God's Holy Spirit. Most of God's children, however, appear to be content to remain as babes in Christ, having a carnal mind that submits to this or that influence of sectarianism, which does keep them from fully understanding the marvelous deeper truths.
I do totally agree that Russell was not a member of the Freemasons' organization. His Biblical use of illustrations of the cross and crown, sun of righteousness, etc., has nothing at all to do with any alleged support of, or membership in, the Freemaons organization. Any such thoughts have to be imagined and assumed. It is totally ludicrous to think that a person would spend nearly his entire life sabotaging what he was supporting by preaching a message that contradicted what he was supposed to be supporting.