Other mistake: When Bruce Banner is loosening his bow tie, he says it's cutting off the circulation to his head. If you look closely, you can see that it was loosely wrapped around his neck to begin with.
Other mistake: The reporter in the opening scene mentions that the Chateau de Shae is 80 floors. The camera then pans up the entire length of the building, and you can see it is nowhere near 80 floors high. It's only roughly half that size.
Other mistake: When Lou Ferrigno is walking away from the reporter, his movement suggests that he is walking on a downward slope, even though he is on level ground. He also disappears into thin air just before he would have stepped out of view.
Other mistake: The reflection of the spotlights in the water in the opening shot does not match the movement of the spotlights themselves. (00:00:01)
Other mistake: When the Leader and his minions are escaping to the rooftop, the bomb detonator says there are only 30 seconds left. After Leader escapes and Hulk goes back into the building to get the bomb, the detonator says 10 seconds remain. While there is an argument to be made in movies and television not being strict with real time, in this instance, far too much happened onscreen for only 20 seconds to have passed. The heroes confronted the villains, one villain tried to talk a hero into coming with them, the police arrive on the scene, a battle happens on the rooftop, the villains escape with the police in pursuit, etc.
Answer: The Hulk is a giant brute who smashes everything in his path when he is angry. In Ang Lee's "Hulk," General Ross, played by Sam Elliot, explains it to his daughter.