Please correct me if I'm wrong, but my understand of the alien craft theory specifically for Oumuamua wasn't just because the object itself was new, but that it changed acceleration [1] without apparent off gassing in a way that isn't explained by our current understanding of orbital physics for a natural object.
It's not just "New object, must be aliens!" It's "This thing doesn't fit our understanding of orbital motion for natural objects, aliens is actually a rational, if still unlikely, possible explanation."
It's not just "New object, must be aliens!" It's "This thing doesn't fit our understanding of orbital motion for natural objects, aliens is actually a rational, if still unlikely, possible explanation."
[1] https://en.wikipedia.org/wiki/1I/%CA%BBOumuamua#Non-gravitat...