If you dig into the UFO reports out there - most of which are much less detailed and documented, but also more various and flat out weird than the ones the Pentagon is giving the thumbs up to - then you start to see parallels and linkage with reports of cryptids, with ghosts and spirits, and with fairies and other historical folklore critters. The "ETs in nuts-and-bolts spaceships with a Prime Directive" hypothesis doesn't really hold up as a general explanation for a number of reasons. But that leaves a much stranger and more confusing phenomenon.