Well they basically disrespected him and his band by cutting his set short. It's like saying Usher's set was more important than theirs by letting it run long and interfering with their time. Just playing devil's advocate, not necessarily choosing sides.
i thought about it afterwards and i definitely can understand why he's pissed off about it. he had every right to be pissed but to drop F bombs and smash his guitar, i think that is when diva billie kicked in.