A native tribe living in a jungle clearing in New Guinea with no knowledge of the outside world but occasionally seeing a jetliner passing high above would no doubt speculate what kind of phenomenon they are. Some, like the OP, would no doubt say that the blobs of light passing high above are just some unknown birds or other natural phenomenona and demand proof that they are anything else. The more imaginative tribe members may say that these could be man made things but then the sceptics point out that the world obviously is just jungle and the few people in it like their neighbour tribes clearly cannot build flying things.

Boy are they in for a surprise....