"I've long wondered if he's been an atheist all along and the experiment was just his was of telling his family/friends."Personally, I rather doubt it. This is one of those areas where the Christian language/perception of "choosing" beliefs becomes, I think, extremely misleading. Beliefs aren't, as a general thing, something we choose; they're conclusions we reach, based on our experiences and the information we gather. Most former believers (at least, the ones I know, including myself) go through a process somewhat like this -- something makes you doubt or question the things you've long expected; you start exploring, looking for answers or alternatives; and, maybe, the answers you find just don't work for you, or make sense to you; and you let go of your old beliefs. It doesn't have to end that way, of course; plenty of people go through much the same process, and find answers that do work for them, and return with their faith strengthened; other find new answers, and return with their faith changed.
Where Ryan Bell differs is that he undertook his exploration in an *intensely* public fashion and explicitly labeled it as "trying on atheism" -- an approach which gave the whole thing an uncomfortable whiff of Publicity Stunt (at least for me, and I presume you as well). But while I think he definitely started as someone who had reached a point where his old beliefs weren't working for him, I don't *think* the whole thing was scripted or that the "ending" (insofar as you can have such a thing, where people are concerned) was a foregone conclusion.
It's hard to tell, of course, when I'm talking about somebody I don't know, and whom I'm only observing at a distance; but I think his exploration was, well, genuinely exploring. I think the publicity-seeking was a separate issue.
I could easily be wrong, of course; I do have a tendency to extend the benefit of the doubt too far. Certainly, one of the comments in his NPR interview ("I don’t think that God exists. I think that makes the most sense of the evidence that I have and my experience. But I don’t think that’s necessarily the most interesting thing about me.") seems a little odd, given that he's clearly put some real effort into making himself publicly known for questioning his faith.