I suspect that the dude went to the park to sleep it off.  I suspect that if he were left alone he would have done that.  Being abruptly awakened in a stupor, he likely reacted with incomprehension of what was happening and likely feared for his life.  Were it necessary to ensure that he remained immobilized, productive police tactics would have been to quietly place blocks and blow out strips behind his vehicle.  Instead based on supposition of potential wrong doing, the police sought to confront.   Confrontation maximizes the chances of conflict and rash action based out of ignorance, fear, or anger.  

This is yet another example of the lack of respect we have for our fellow citizens.  There were others ways to constructively handle the situation that would have minimized possible conflict.  We simply do not care enough to make the effort.  And we wonder why we have mass murderers?  We teach that others are to be put down if ill perceived.