The UFO nonsense was crafted in the 50s to explain crashes and flights of top secret military craft. And the rest is nutjob history...
Recommended reading for you:
https://www.amazon.com/Passport-Magonia-Folklore-Parallel-Worlds/dp/0809237962
UFO sightings and alien sightings and even alien abductions have been a part of the human experience since we looked out from a cave after we finished throwing feces at each other.