I'm aware of that story/narrative, but I draw it into question.
The classic means of counter-intel is to use grains of truth to sprout a narrative of falsehood. The Germans were very interested in genetics projects as it related to humans and had an interest in ancient archaeological sites.
I don't think we are looking for extra-terrestrials or UFOs. At least, I think those are largely distractions to obscure a greater truth that is closer to home. Consider Knights of Sidonia, or Sidonia no Kishi. A multi-generational ship that set out from 'Home,' fleeing an adversary which destroyed that home (Earth, for all intents and purposes). After an attack kills most of the ship's crew/population, genetic banks and clones are used to repopulate the ship while a council of medically-induced immortals rule over it's society.
The point being that there may be much more going on than simply a random rock sprouting sentience and then a pack of alien inbreds happening upon it.