He did speak about it. To paraphrase, he basically said that when he had voted against her earlier he thought she was out of the mainstream, but now that he had a chance to sit with her for an hour and review her congressional testimony he’s decided that she is in the mainstream. Also, he said that she’s smart and qualified and he wishes her well.
So, no major revelations that caused him to change his mind. Just “she convinced me she’s not as crazy as I had previously thought”.
(And, no, I don’t think this is sincere. The theory that he might run for President again as a centrist makes sense. I proudly voted twice for Obama, but I thought Romney would do a good job as President were he elected)