UFO's are demonic, just like ghosts and all that other new age BS.
Not being able to identify a flying object does not make it demonic.
How can one know the nature of something one cannot identify?
New Age BS is...BS. It does not lead people to God, but it is not a demon.
St. Paul in Scripture addresses the nature of idols:
Now concerning those things that are sacrificed to idols, we know that we all have knowledge. Knowledge puffeth up; but charity edifieth. And if any man think that he knoweth any thing, he hath not yet known as he ought to know. But if any man love God, the same is known by him. But as for the meats that are sacrificed to idols, we know that an idol is nothing in the world, and that there is no God but one. For although there be that are called gods, either in heaven or on earth (for there be gods many, and lords many).
Yet to us there is but one God, the Father, of whom are all things, and we unto him; and one Lord Jesus Christ, by whom are all things, and we by him. But there is not knowledge in every one. For some until this present, with conscience of the idol: eat as a thing sacrificed to an idol, and their conscience, being weak, is defiled.
Treating idols as if they were real beings was a sign of weakness and ignorance. It was to avoid scandalizing people who were so ignorant and weak that he advised not to eat such meat, however, the idols are stated as being "nothing".
Now, if an idol or other false "god" reacts, interacts, or otherwise shows power, it is a demon, but human creations are nothing.
"Aliens" are a popular culture creation, based on TV shows and human desire for entertainment. It appeals to many, and the mentally ill, confused, or otherwise not rational people may make claims about them.
If some being exhibited unnatural abilities, then we could be suspicious of demonic activity, but to treat these things as legitimate phenomena is not proper or rational.
We cannot treat the popular conception of alien activity (inter dimension beings, etc) as reflecting any sort of reality. It is Pokemon essentially. Human imagination and entertainment.
If we had evidence of a fire breathing lizard evolving into a winged dragon-like creature, then we can suspect something, but otherwise, it is a human game, not to be taken seriously in itself.