Honestly I'm thinking a deformity or some kind of little growth. It's not hard at all, just fleshy. That spot has always been a little lighter in color, but slowly growing. Can't find anything online about bumps like this one, though, that's why I'm concerned.
He's never been fed live, so it couldn't be a bite, and he's never been injured, but maybe could have scratched that area on a piece of coconut coir or maybe some of the cork I used to keep in with him? But, I've never noticed an injury, and he's a healthy little guy otherwise. Vet visit looks like it's in the cards just for my piece of mind. Really hope it's not an infection or some kind of tumor.