You better start adding fairies, elves, bigfoot, the loch ness monster, witches, werewolves, etc. to your list of phenomena then. All have eyewitness accounts, published books, research papers (of a sort), and long documented histories. I don't believe any of them are true, do you?

Any sufficiently advanced technology.

The human capacity for reasoning and deduction has been relativly unchanged for a long time. The ancient greeks proved this.

These are evidence that some manipualative memory screening technology is capable of playing into the current belief systems. Goblins from the dark ages.

The question is, does this false memory screening originate within the human psyche or is it external? There is ancedotal evidence for both, proof for neither.

Are you suggesting that our technology is being reverse-engineered from captured alien spaceships or that our technology can be advanced by capturing one?

I doubt that very much. Our advancements seem to originate from the hard work of dedicated researchers. Further, every technology we have has a parallel somewhere in nature.

If there were an avanced technology being employed that were capable of manipulating perception and memory, then. Recovering captured technology from us would be an easy application of such.

There is ample evidence that defense research has taken some unusual turns. Remote viewing was one. I do not think any possible avenue would be ignored. Defense by definition of objectives would have to consider all possibilities or risk extremly unpleasent surprise. All such research by definition of purpose would be classified.

It all again comes down to one question. Are the extraordinary reports that just keep coming in of internal or external origin?

The photos and vids I have seen suggest external. The lack of physical evidence suggest internal. The answer remains unresolved, but if it is like most things I have observed, it is likely some of both.