I thought Rosen said "staccato gunfire" and "bam bam bam bam". A couple of shots could be consistent with hunters (not at a SCHOOL, but generally). What he describes isn't really like that. But, personally, I don't think he heard gunfire. I think he didn't know anything was happening until he located the kids in his driveway. I think he elaborated later. But, like I really know wtf he's thinking.

As for the janitor, what I read is he was trying the doors to be sure they were locked. I just figured he didn't want to be interviewed initially so the media latched onto Uncle Gene. But, IDK about that either.