Dan at the end knew

Good question you brought up, and I like it. I am still undecided whether to use the word "cave in" to its fullest extent. To a degree, maybe, he did. For me, this is the pivotal and turning moment of the whole movie. John, the caveman/Jesus Christ, shook every person's beliefs. To some, like the Catholic professor, her entire being. I think John decided to reveal himself, because he appreciated them dearly. He thought, maybe, that being the intellectuals they were, they would keep an open mind. John would be able to convince them and make them accept the truth and even like him even more for revealing close personal information. Maybe that would bring them even closer together. It was an excellent opportunity. He, unfortunately, took the chance and lost. Now, after he left, he will be remembered as somebody insane, or who at least, made a horrible scene and joke before leaving.
It turns out that revealing the truth wasn't worth it. They were, just like many people in the world, incapable of grasping and wanting and accepting the "hurtful truth", and instead, prefer or preferred living a joyous fantasy. The religious professor, and the others, started to reprimand John rather than keeping an open mind and continuing with the intellectual discussion. For example, the Catholic teacher asked John something,"Why, after these years, do you do this to me? You know, I'm Catholic?". It was as if saying, "How dare you? You know what I believe in, so why do you question it? I don't change my opinions, even when I'm presented with new evidence". It was sad and disappointed to see this coming from the Catholic professor. Once John noticed how she and others were reacting to his story, he knew it was not worth continuing arguing with them. Anyway, I loved the whole movie including the acting.