Other mistake: When the forklift driver gets distracted by She-Hulk and crashes into the stack of metal vials full of flammable liquid, Bruce and She-Hulk don't hear any of the commotion until the explosion happens, even though they are only a few yards away. The crash and the falling metal vials should have been loud enough to alert them.
Other mistake: When Bruce Banner is sitting on the dock and recording his thoughts on a tape recorder, you can see that while his reflection's mouth is moving, his actual jaw is not.
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.