As dumb as it MAY seem....he may have done a good deed.
I think the correct response would be to keep the kids off the rocks in that case.
It wasn't a kid, it was a 200+ lb. man who had to put all his force into pushing it down.....That rock wasn't about to fall anytime soon.
Of course it would eventually have fallen by itself. Maybe have been many years in the future, but nothing lasts forever right?. To push on it to destabilize it and make it fall is simply vandalism.