What is plausible isn't the right question, after all, in the almost infinite expanse of the universe (and infinite probability theory as some physicists study), anything is plausible.
The right question is, what is probable? It is plausible I win the Powerball lotto and date Kate Upton on the same day. It isn't, however, probable to any reasonable measurement factor.
This really is a thought experiment for those who are coming on the thread weighing what is said. Start writing out the probability. Whether it is the probability of aliens in the traditional sense, the 'Biblical fallen angel' theory Quix proposed, or a cover story to hide top secret military testing, or something else.
Which of these fall even close to the level of reasonable probability
I don't know how one would assess with even relative assurance that one had a comprehensive enough grasp of the relevant data points involved to measure such probabilities with anything remotely congruent with "reality."
The Drake equation, as Stanton Friedman royally trashed . . . is a farce from the git-go.
In terms of evolution--the universe has not been remotely close to in existence anything near the time 'required' for such 'evolutionary' probabilities to have a ghost of a chance of operating.
And the probability that life sprung spontaneously from nothing is far, far, far less than one in the number of atoms in the postulated multiverse . . . in other words . . . in probability terms . . . impossible.
I just find your whole leaning on the probability argument extremely lacking in terms of its reference to sufficient data points involved.
ADDED:
However, when one looks at the 10's of
thousands of pages of documentation included in the DVD to the print copy of EXO-VATICANA . . . then the probability that their explanation
best fits the data points available . . . approaches
certainty, imho.