First of all, that charge would amount to a simple assualt not in the presence of the officer (misd), so he couldn't arrest him even if he wanted to. The jack ass would have to place him under citizen's arrest and sell the story to the cop. If the cop believed him (*which he/she most likely would not), he would be issued a cite and given a court date to show up. The good news, or bad news possibly, is that the jack ass would then be civily responsible for the arrest. Meaning, that your bro could sue his ass for false arrest after the case was dismissed, as it would be by the DA due to lack of evidence. Contrary to popular belief, most cops are not idiots and can look at a situation and pick out the most logical situation that occurred.
I think if the story is that your bro actually tried to strike clown, he would probably be missing a jaw right about now. In order to believe the neighbor's story, the cop would have to believe that your brother intended to assault the dude and failed at it. Not bloody likely.................
The cop probably told him that to prevent him from carrying on the altercation. As far as the dog, I would take the recoomendation of the civil rest order route. One other avenue might be to try animal control. They have strict criteria and you have to record the dog barking at various hours within a time period, but they will eventually take action.
Tell your bro to stay clear of this clown as he might be baiting him to do something and then come after him with a civil case...... Just my .02