Dunno, if kids kicked me in the ribs as I rode by, and I had a gun on my person, I'd be inclined to use it. Getting kicked off your bike at speed could result in a very serious injury, and I'm not going to say that responding with deadly force couldn't be appropriate.
Though if the kids were fleeing and over 200 feet away when he fired, it's going to be very hard to claim it's self defense.
At least in Texas, when you get a CCW permit, you have to take a class that goes over in great detail when you can and can't use your gun, and what the penalties can be. I imagine other states are similar ...