The exact details of what did or did not happen may never be known. The video and a few generalized assumptions should suffice for most. Here in the DR, the police are unpredictable in their conduct. Here in the DR crowds are pretty predictable - there is a good likelihood that there will be a "disturbance in the force" eventually. Bringing alcohol, a party atmosphere, a crowd and the police together at the same time is a recipe for trouble.
When out in public, especially on holidays or at events and venues that draw groups of people together, you need to pay attention to what is going at all times. You need to be ready to duck, run or just decide to leave. It's not often possible to know the future, but generally speaking we all can determine for ourselves that where we are may not be a good spot to remain.
You especially need to keep an eye on the cops. Where they are, is generally a potential flash point for circumstances to spiral out of control. Bullets, travel at 1200+ feet per second. You don't need to be in the middle of the mix to have a really bad day from one second to the next.