Most of the time, fin biting does appear like mouth-shaped bits taken out of the fin but on a few occasions, I've had my bettas literally shred their fins into ribbons. So it's a tossup. It's not typical fin biting but I don't see the thick blackened edges I'd expect to see with a bad case of fin rot.
In this case, I'd go with homegrown terror. Fin rot or fin bitting, the warm water and 1 tsp of AQ salt per gallon (or alternatively, API Stress Coat or another similar product) will help the fins heal. If, even with the treatment, the fins continue to degrade, you can try changing his decor around or adding a new plant or hidey hole. If he stil continues to have ratty fins, then we might be looking at some other cause. But so far, he looks very healthy to me. :)
High protein foods also help with fin regrowth so if you have frozen bloodworms, feed him plenty of those.