An excuse? Not at all.
What this kid did is not much different than a cop staking out a bar and pulling over drivers who have just left (with a valid reason, of course) and doing a Breathalyzer.
They deserve their DUI, yes?
Of course. But something tells me you wouldn't be at this site defending the drunk driver by saying that the cop was probably driven by a personal desire rather than public service.
Your tendency to argue the side of the law is useful in many of these threads, keeps people sharp on the other side. But in this case it is pretty clear that the law was wrong. You admit that the officer was in the wrong. But if the kid didn't run the camera, the officer would have gotten away with it.
The bottom line is that the officer serves the public, you, me, and the kid. In his role as public servant, the officer has zero fourth and fifth amendment rights from the public that they serve. Their role is absolutely public, and can be monitored and recorded for any reason at any time.