He didn't have a muslim faith so he doesn't have to renounce it. He wanted to make a record of what happened and knows better than you that he could well be a target again for doing so. It appears to me he is willing to take that risk and thus publicly announced that he is in fact a Christian.
Rejoice.
I don't know --- what does it take to become a muslim? You have to submit --- and it seems at least for the moment he submitted. It's not like they have Baptism or anything official --- just that submission. I wonder how they -- the muslims view it --- you can't "unsubmit" once you've submitted, I think he's probably under a death threat for the rest of his life.