Dog abuser

I had a run in with a real jerk this weekend at Birch Bay state CG in Washington state.
He would walk his dog, a large full grown German Shepard mix, around the park and and jerk his narrow leather collar (not a harness), so hard the dog would be jerked off its feet and land on it's side or back.
He did this by walking by the dog and then stopping while the dog continued on. Then he would brace himself and jerk backwards as hard as he could. The dog would let out a yelp like I've only heard when someone steps on their paw or hurts them in some similar way.
I called him out on it and told him to knock it off or I'll call the cops. He said "go ahead" but then thought twice about it and tried to tell me he was a "trainer". I told him he was a liar and that no professional trainer would do such a thing. Every time he addressed the dog it would cower and put its ears back. The dog was terrified of him. The dog was also perfectly behaved.
I'm not a violent person (haven't been in a fight since Jr high) but I wanted to knock this cowards head off. I think I got the message across though as I didn't hear him hurt the dog again.
I did tell the Ranger but nothing became of it.

So was I wrong somehow?
I cant see how such abuse is ever acceptable but I'd like to hear your thoughts.

PS, it still makes my blood boil to think about it.