Let me ask a question:
Do you mean to say UFO sightings are non-real events, or that merely the names given the events differ based on the level of technology (or culture) that existed during the event?
What I am saying is that crazy people throughout human history have claimed to have seen some pretty crazy stuff.
Back when nobody thought of the possibility of technological flight and extraterrestrial intelligent beings, the crazy things that crazy people claimed to have seen didn’t include such things; but instead included glowing mystical figures, flaming chariots, beams of light, a shower of golden coins, etc.
Only now that people are aware of the possibility of interplanetary spacecraft of alien life does the crazy things that crazy people claim to have seen include lighted disco disks and bug eyed aliens.