<<<Regardless, could an LEO do such a thing?>>>
We have to look at the facts. The police were called, they just didn't show up. There was a complaintant. There was an argument, and one of the persons arguing continued that argument with the police. Actually, I'm surprised, reading your scenario, after the subject was told to move on, that he wasn't placed under arrest for obstruction of justice or creating a disturbance.
[or] To carry it one step further. If the guy refused to move on, the person could be arrested for creating a disturbance (or as we affectionately call it, "misdemeanor stupid") the vehicle impounded and the dog sent to animal control. The officer could state the dog appeared "out of control". At that point, Animal Control could well test the dog. Seems far fetched, but could happen.
DFrost