I could write an essay about how difficult this horse's face was to caricature. I learned that outside of a few very select breeds, it's really hard to identify a horse breed by it's head alone. Really, for the Quarter Horse, you need those powerful muscles and hindquarters or else no one can tell what breed it is (not even me)!
Actually I have seen real life Quarter Horses that look just like this. Maybe they give them steroids too much? XD Some Quarter Horses are built like Thoroughbreds, others like Arabians and some like Belgian Drafts. I think QHs are one of they most varied when it comes to body conformation. Most of the ones you see at horse shows have big butts and tiny heads. LOL I myself prefer the ones that look like a Thoroughbred but shorted legged and thicker bodied.
You properly saw a horse with HYPP. It's a genetic disease that makes the horse look extremely muscular and gives them multiple problems with their muscular and nervous systems.