That is correct.
Their invocation of the multitude as additional witnesses is hearsay. That is why I originally stated that the witness accounts for Jesus is actually very low, restricted to only those who wrote first hand accounts in the Bible. (Let us forget that none of the New Testament was actually physically written by the Apostles. The material appears to have been created in the 400s.)
In one case, people want to believe while in the other they don't. The idea of ET offends people's desire to be God's center of attention, I'd guess. Me? I laud and praise God for His gigantic and well-stocked Creation!
The witness accounts are still more than for any other person in antiquity. More than Hannibal, Alexander the Great, Caesar , Cleopatra, Mark Antony, Socrates, and scores of others.
All of the New Testament authors were known from the beginning except Hebrews as far as we know. I have no idea where you got the 400 ad date. Papias confirmed the authors of the Gospels and he lived in the first and second century. Further, I know of nobody who claims an alien encounter that also claims there were scores of witnesses to the encounter,