Doesn't this boil down to "If artificial intelligence wasn't artificial, wouldn't we just call it intelligence?" which feels like a tautology dressed up as a thought experiment.
"What if we encountered an extraterrestrial life form which had independently developed anthropomorphic tendencies" is a totally different question from "What should we think when we encounter a heavily engineered system designed by humans to be anthropomorphic?"
If a human-looking alien came out of a UFO, it would shake my worldview even if I realized it was made of tissue closer to plastic than human tissue. I don't feel the same way when I encounter a doll in the toy store.