Not really. More people have died in car accidents in the last 100 years than by stingrays. Stingrays are not considered dangerous or aggressive animals.
I understand he was hovering right above this huge ray and his cameraman positioned himself in from of the ray (blocking the rays egress in the process) for a better shot and that spooked the ray and it defended itself. Steve pushed the outside of the envelope once again but this time it pushed back.
I respect him but having taken risks in things myself in my youth, I see it as not unexpected and he finally lost one.