How dare you?! You and I are through!! 
I'm thinking that it was like so many crowded arrest events and without information to the contrary, will assume that EPD did their job. Don'tcha know that cops love arresting people???
I doubt that EPD hustled the girl into the squad car and sped away. So, they arrive, try to sort through who did what. As they're making the arrest, her friends are yelling Pigs! Facists! and, feeling emboldened, are bravely crowding the cops. Man says Hey, that's uncalled for. Girl is in car, police assess the situation. They have NO right to tell everyone to leave. People shuffle away. Show's over. Assoles decide to take out their anger on the good sam. Who'd have seen that coming? 
It will be interesting to learn more about this as info becomes available.