That is crazy! It's like something out of a science fiction movie. No, I can't say this is normally how they heal a big rip like that. Usually, you will begin to see clear growth around the edges of the tear that grows down until it is the same length as the rest of the fin, then it colors in to match. I think your guy is radioactive or something.
But that said, the powers of fin regeneration are amazing so I guess anything is possible. I mean, fin regeneration can happen in as little as a week. It's just the particular way your guy did it, filling in the hole like that, is unusual. Really unusual.