I agree with him. It is their job to ensure that protests remain peaceful. So it makes sense that he would join with them. The only question remains why they couldn't at least attempt to keep the protesters 6ft away from each other? Though, they were probably afraid of it escalating if they did that.
Indeed, I think it's a good answer. But it doesn't explain why Mayor Coles was there, and even more troubling, OC Prosecutor Billhimer. He is in charge of upholding the law, but he is not a field law enforcement official.