He was willing to change his lifelong belief (or lack of belief) when it was contradicted by evidence, as he saw it.

He describes it rather differently: "This was not a case of defense and prosecution laying out evidence for my reason to pick through: I was altered down to the root of my being."

He later speaks of evidence, but what he takes as evidence is religious visions not further described. Whatever this experience was, on his own account no process of rationality played any role in his conversion.

It is scary that someone can get such severe and convincing hallucinations at the drop of a ventricle. (Edit: on further review, he was taking atenolol during at least part of that period, which can cause hallucinations.)

I didn't notice the philosophical buildup in the version of his conversion story that I read. It's there, but brief. In this article, he plays up the significance of his personal religious experiences.