Continuity mistake: When the Hulk throws the tire during his second transformation, the first shot shows a horizontal trajectory but the second shot shows a 45 degree angle trajectory, which makes the tire land much further than expected.
Continuity mistake: When David is leaving at the end, he is wearing a blue shirt under his coat. Moments later, he removes his coat but he is wearing a different color shirt with a square motif.
Continuity mistake: When the Hulk throws Mr. Malone in the river during his second transformation, the first shot is too long and we see that he would fall a few feet from the closest river shore. But in the second shot he is flying like crazy and almost lands on the remote river shore.
Answer: The Hulk is accused of killing Dr. David Banner and Dr. Elenia Marks. After the lab explodes, McGee sees the Hulk emerge carrying the body of Dr. Marks, so he assumed the creature is guilty. It was McGee who caused the explosion. After following the trail of evidence of the Hulk to the lab, he hides when David and Elania arrive. In a darkened storage closet, he knocks over a bottle of flammable liquid. He confronts them, then is forced to leave by Banner, who says, "Don't make me angry, you wouldn't like me when I'm angry." When Banner reenters the lab, it explodes, caused by the Hulk when it went on a rampage trashing the lab, causing many electrical systems to catch fire, thus igniting the flammable liquid.
The Hulk didn't cause the explosion. The liquid mixed with another chemical. While David and Jack were both outside, Elaina heard a sizzling noise, and when she saw smoke coming from the closet Jack was found hiding in, she called out to David. That's when the explosion happened.