Your guess is as good as mine. The simplest explanation for why Grusch’s testimony matches the general UFO lore is that… the basic story is true: the presence of aliens, the reverse engineering, the coverup.
It’s not the only explanation, for sure, but I can’t think of any parsimonious way to explain why so many people whose jobs would plausibly five them access to this sort of information have been repeating the same story over the decades.
It could be a cult, but by whom, for what ulterior purpose? And how would this hypothetical cult convince high-ranking officials to join them?
Like I said, I can’t think of a coherent alternative explanation. Aliens may simply be true, weird as it sounds.