I'm thinking either that, or they do something like they did in the comics with Onslaught where Banner is "turned off" completely through some physic means (In the comics it was Jean Grey who did it, I think. Been a while since I read it, and I have no desire to revisit it) and he becomes "pure" Hulk with no Banner to hold his rage in check, and thus absurdly powerful even by Hulk standards.