can thousands of them be 100% erroneous
In short, yes. In a country of hundreds of millions of people, finding thousands of people with any shared characteristic is not surprising. As faul_sname said, I would expect at least hundreds of thousands of people to be eyewitnesses to anything happening over a major city.
Independently, our current knowledge of physics strongly suggests that interstellar travelers arriving in this solar system would be visible (during deceleration) to any serious observation of the night sky, whether Mayan, Ptolemaic, Galilean, or modern. The absence of any record that suggests arrival is strong evidence against interstellar aliens.
Many of your points are not primary evidence though.
Primary evidence includes eyewitnesses. And even if it didn't, the secondary evidence is so strong that total absence of relevant primary evidence is irrelevant.
You asked elsewhere why you are getting downvotes, and the brief answer is that you are dramatically over-weighing the strength of the relevant evidence.
Recently I've been struck with a belief in Aliens being present on this Earth. It happened after I watched this documenary (and subsequently several others). My feeling of belief is not particular interesting in itself - I could be lunatic or otherwise psychological dysfunctional. What I'm interested in knowing is to what extend other people, who consider themselves rationalists, feel belief in the existence of aliens on this earth, after watching this documentary. Is anyone willing to try and watch it and then report back?
Another question arising in this matter is how to treat evidence of extraordinary things. Should one require 'extraordinary evidence for extraordinary claims'? I somehow feel that this notion is misguided - it discriminates evidence prior to observation. That is not the right time to start discriminating. At most we should ascribe a prior probability of zero and then do some Bayesian updating to get a posterior. Hmm, if no one has seen a black swan and some bayesian thinking person then sees a black swan a) in the distance or b) up front, what will his a posterior probability of the existence of black swans then be?