With your background in law enforcement, tell us how, in your expert opinion you'd have handled this? The old man committed no crime, but the cop did.
So with your bright(?) legal mind you're saying it's legit to make a citizen's arrest of a driver who is, in fact, not drunk and there is no evidence to support him being drunk? All you have is a disoriented 70 YO man involved in an auto accident. I think I can see why you changed careers.
You're an internet tough guy, but there are a lot of people out there I'd love to see you try to make a citizens arrest for a simple auto accident where they are in fact not drunk.