That was most likely a bonnet head. They are literally all over the place.
Anywhere there are decent grass beds, there are bonnetheads.
If you ever want to catch one: take a live blue crab, crack its shell, and cast it out on a number 5 long shank hook with some 50 pound mono leader or just wire leader.
Best bait in the world for these guys. The smell of the crab drives the bonnetheads into a "search frenzy" . It's pretty fun to catch them and if you are in shallow water you can watch as several of them circle around and finally hone in on your bait.
They are pretty harmless. Just use some common sense when removing the hook (or just cut it off and put on another). The hook will rust out or come out soon enough.