Other mistake: In the scene where the mutants are confronted by the police on Bobby's front porch, there is a male officer to their right and a female officer to their left. If you watch, you will notice they are aiming their guns directly at each other.
Other mistake: During a closeup in her fight with Wolverine, Kelly Hu's contact is not on straight, making her pupil not the center of her iris.
Answer: Presumably he is sensing the presence of Jean/Phoenix.
BaconIsMyBFF