Don't brush Bojack's comment off too easy PZ547.
Most of all the Vampire, Goul and Living Dead perceptions have been easily explained by Medical interpretation and evidence.
People who know no better do come up with their versions (fear based, of the unknown) and thus the Vampire legend grows.
Be it the sound 'dead' people make because of the gases in the 'dead' body slowly going off. But to the people of the past, it's a dead body ...living again.
So it is with Aliens.
Like I said above. It's just a 'mascot' mythology being driven by the New Worlds in comparison to the 'Primitive' Caveman of the Old Worlds.
Look at the USA: People attend Cinemas, as if they were Holy Temples and there they watch their 'Heroes & Gods' there on the big screen. Superman - the ultimate 'Hero-God' of America.
In time, with each generation - that mythology becomes more ingrained to the point of being 'believed'.
Loch Ness Monster is a good point of people 'wanting to believe' (there is a mental condition that even relates to large groups of society ...but I forget the term) and 'needing to believe'. Hell, how many kids films go on about "If kids don't believe - then Santa and Fairies ...just disappear." - quite a few.
So no. Aliens are not 'Demons' (Demons are Demons for starters).
Also - people of North America are very 'Air/Sky/Heaven' orientated. Hence why they are the best in the air during wartime, won the Space Race and have the Bald Eagle as their symbolic Animal spirit.
(Sadly for the Amerindian - wearing feathers and chanting "I am one with the sky spirit" just couldn't compete with the Wright Brothers version.
So 'Aliens' from outer space is another MAN-MADE entity to both be a carrot on a stick and other things, especially from the USA (where it started).
Many Americans claim the 'Light in the Sky' for their inspiration to better their lives, find spiritual fulfilment, etc.
This is why North America is more closely associated with the Middle-East than any other region: it's a 'Heaven' thing and as you can see ...aliens come from above.
As an Australian, even I could rouse up Megladon stories (which originated from Australia and took the world by storm a few years ago) and other 'down under' the ocean stories. Maybe coin a few more 'Mud Sharks and Drop Bears' waggling tales.
As a Diver - even people's perception of me could manifest 'future dream'-like by others as advanced 'Aliens from the deep' (Abyss).
Cargo God anyone? (PNG tribes)