Jessica Might Be Confused About What Genre of Music John Mayer Actually Plays

"She was rocking out the whole time," says one concertgoer. "She only seemed to know the words to his older songs though, because she sang along to 'Your Body is a Wonderland' and his older hits."

With a camera in hand, Simpson – who took in the show from the sound and lighting area alongside stylist Ken Paves, Billy Joel and his wife, Katie Lee Joel – snapped photos of herself and Paves, Mayer and the crowd.

"She was dancing like she was a real fan, and a lot of the crowd had their eyes on her the whole time," says the observer.

Source: PopSugar