So let me see if I follow. Asian guy gets in a road rage incident (not acceptable, but happens) but the people he thought were civvies he was road raging on were off duty cops. They call it in, and this guy comes across him, pulls him over for the road rage incident and just proceeds to whip is ass as soon as he walks up to the car?
No matter what the Asian dude did earlier, this is a CLEAR case of excessive force. The douche bro cop IMMEDIATELY starts after him after telling him to get out without any chance to get out.
I'm not a cop but I would think the proper way to handle it, even if you were in fear of the guy having weapons based on teh previous road rage, would be for each cop to approach from opposite sides, weapons possibly drawn but command him to get out and lay down and then approach him. Can any LEO here tell me if that's more likely to be normal protocol?