During General Vezax in our 10 man raid, we had 3 instances where a melee was randomly targeted by Vezax and killed instantly. 1 instance was our Enhancement Shaman and the other 2 instances were our Retribution Paladin. Neither players were even remotely close to pulling threat off the tank. As far as I’m aware, there isn’t a threat drop/wipe mechanic for that fight either.
I see this happen on a regular basis. Ret seems to be the most common class getting targeted on pull.