Sometimes a kid (or any person) just doesn't like where they are at...not in a negative way at all but they just want something different. I think we have all been there before.
Anyway, back to the original issue of him leaving. I still don't understand why you just don't gut out the rest of the season and work your tail off. Even if you're planning on leaving, you could still have the perks that come with being part of team, even if you don't feel like you're being treated fairly, and still be staying in good physical shap. He'll do well in FCS, but he doesn't have too many more chances to show his stuff, so better make the most of his next home.
Also, to your point of not being restricted. The rule took effect AFTER he got his release. He should have just waited. Quitting was so damned stupid.
It does sound like Bell misunderstood the redshirt rule, and how it would impact his transferring. Either way, I won't begrudge people and their decisions. Maybe Bell realized he wasn't cut out for the hard work and struggle that big time, D1 college football at a big school can be. Maybe he would rather go to a place where he can be a big fish in a small pond, and excel at a smaller school. There is nothing wrong with that. It's very similar to people who like living in small towns because they like being a "big fish" and want their kids to have similar opportunities.
He was in pole position to be a big fish in a big pond. There are so many stories of successful players of the last that only found that after having to struggle and persevere.
This transfer happy craze is denying that to so many these days.