Was this a dumb thing to do?

Just got back from two weeks in Puerto Vallarta. Didn't swim much (still with a bum shoulder). I really only swam once, and it was a very short swim. My mum-in-law has a time share (week five, always the same unit). She got a bonus week (week four, in a different unit), so for a couple hours after vacating the first unit we just hung out under a gazebo by the water. We're sitting there and someone calls out about some whales. They were way off in the distance, but in the foreground we also noticed a fin flapping around near a line of buoys which runs parallel to the beach. I think it's intended to keep the dumb jet ski types from hitting some pretty shallow rocks. Anyway, we watch it a bit. It disappears, then reappears, flaps lazily every now and then. The buoy line disappears, then reappears, moves around a bit. A crowd gathered to see what we sort of thought might be a whale caught in the line. A lifeguard walked out to the end of a small jetty, took a look, then left. Same with a pleasure boat near shore. At this point it's pretty clear this animal is in distress, maybe drowning. I never saw a snout break the surface. A security guard was keeping people back from the end of the nearby jetty. I went out and asked him what he was going to do. All he cared about was keeping people back. Another staff member said it was the Federales' responsibility. I was fed up and hopped in and swam out to the line, maybe 20 yards. The tide was in so the submerged rocks didn't cause any problems. Once I got out there I managed to get one loop of the rope off what turned out to be a manta ray. The rope was wrapped multiple times around his left horn (proper term?), just in front of his eye. I couldn't do more. I expect he might have thrashed around a bit when originally snagged, making his predicament worse. After a couple minutes a lifeguard with mask/fins/snorkel comes out and another guy on a kayak turns up with a large, very sharp knife. The lifeguard managed to cut the rope in a couple places to free the fish while I backed away from the action. The ray was freed, everyone clapped a bit, then went back to their beers and suntan lotion. While it was a heat of the moment decision, I never felt like I was in any sort of danger. There were no waves or strong currents, and the ray was pretty listless when I got out to him. I certainly didn't feel like he was going to thrash around and hurt me. I saw no other fish (like sharks with teeth) around. Was it a dumb thing to do?