Yes it does sound like fin rot, but worry not, it is easily curable. My fan tails are very prone to it and look very ragged most of the time! Even smaller pet shops should stock at least one variety of cure, bigger places have lots of options. Most of them you can just add straight to the tank, and don't need to worry if there are other non-affected fish in the tank. You need to act before the 'shreds' reach the fish's body as this is when serious probs can occur. Otherwise, the fish should be fine and the shreds should stop getting any closer to the body. Mostly they heal pretty well too. There'll be plenty of medicine left if he gets it again too.