“...that any creatures arriving which presented themselves as aliens could only be Satanic demons in disguise.”
That is a pretty common view and quite a valid one with respect to the UFO phenomenon and associated sub-culture.
It really differs very little from occultism or other sort of supernatural obsessions and beliefs.
If one doesn’t believe in demons, then understanding it as hoaxes, charlatanism, weird beliefs and mental illness suffice.
But the above has nothing really to do with the topic of this thread which is a hypothetical examination of what religious would say if actual real extraterrestrial intelligent life were known.
Yes it does have everything to do with this topic of this thread.
I can’t speak for other religions but the book of Genesis of the bible in chapter 6 talks about these beings the fallen one, that’s where the word Nephelim comes from, the fallen ones: the fallen angelic being who are demonic in nature.
You ever seen the early 1970s movie: Chariots of the gods (spelled with a little g , for the ancient peoples considered them as gods ).
The whole world is filled with evidence that they where here.