Section bias seems like a misnomer for this situation. It'd be selection bias if grainy blurry alien videos were more likely to get popular than high-def ones. There doesn't seem to be any kind of "selection" to be biased here.

The selection occurs when hi-res videos depict so clearly what is actually going on that it's revealed to be some mundane event, and doesn't even qualify as a UFO any more (even if it were positively identified as an alien spacecraft, in which case afawk it remains classified)

The reverse argument is that if blurry evidence of aliens exists and aliens are real then there is also lots of extremely clear evidence of aliens that has never been released to the public. I find it unlikely that we haven't had a leak yet. The reality is that this extremely clear evidence and the aliens that it is supposedly depicting simply does not exist.

Also, if it were the case that the intelligence community had very clear evidence of aliens, they would be extra cautious about the blurry evidence they release. Also, it would be a huge statistical anomaly that either civilians didn't catch some of that clear evidence, o that intelligence are actually that proficient in doing global cover ups.