Hi, it's very possible it could be fin blowout, it depends on how much he has been flaring.
His tank does look a little sparse and with him being under the bright lights, he can get stressed. You can supplement the tank with some silk plants and replace them as you go, these little guys like to swim in a little jungle. It would help him calm down a lot if he had someplace to hide when he wants. A small terracotta pot on it's side can make a good hide (just be sure to plug the hole in the bottom). I also made a coconut cave, but that's just because I wanted to try.
You will also have to just try and see what works for your betta, there's no telling what they will like and use. I've given mine cups, terracotta pots and the coconut caves and they use it sometimes. My Saffron currently would rather stuff himself behind the sponge filter than use the cave. Here is he, instead of using the pot, he chose to hide under the IAL that sank ontop of the pot.
Your fish is a beautiful little guy.