Well honestly if I were you I'd start the search for another trainer, it doesn't sound like this one is very breed knowledgeable. First off pit bulls aren't "taught" or "trained" to fight anymore than labs need to be taught to retrieve or border collies need to be taught to herd, or hounds to follow scents, it's what they were bred to do and any pit bull regardless of upbringing may be dog aggressive or fight with other dogs. It also has nothing to do with human aggression, there are many dogs from fight busts who are wonderful with people, and some who live with other dogs too. Pit bulls love to grab and hold stuff, if your dog didn't drop the leash, it's probably because he's never been taught a drop it command or was too overwhelmed. You said he was told "no" but dogs don't understand "no" means drop the leash, don't jump on counters and a zillion other things just because we say it, they don't speak english. Is he aggressively biting? A lot of pit bulls are mouthy and haven't been taught inhibition, but it's impossible to say without being there. As far as his growling, is it when you feed him or what?