I once witnessed an accident where a woman driving a small car got knocked out and had her skull exposed when an overhead traffic light crashed down on her. Looked horrifying, but she ended up being okay. Convulsing doesn't prove anything about severity the injury, other than that it hasn't killed the person (at least not yet). People survive this kind of thing all the time. He's probably young and physically healthy, like most of these "protestors", so less likely to die or suffer permanent brain damage.