If we abstract away the specific actors/motivations, this reminds me a bit of the Oumuamua debate. "Man made" and "natural" are both very broad theories that admit many details and are thus hard to falsify. But I wonder to what degree we agree about:

(1) Which category (if either) has an advantage by Occam's razor? (2) Which category (if either) is more easily falsifiable? (Meaning easier to determine improbable, since it is hard to falsify them entirely)

For me, I see neither having an advantage on (1), but on (2) there are a finite number of relevant, well-known lab techniques that could be investigated.