To get a CCP? I'm not a gun guy. In any case, the instructor might well have been using this as a perfect opportunity to drive home the point to every other member in the class. IOW, if that guy had been the sole student, he would have merely gotten a severe talking-to.
Perfectly valid technique. Could well have staved off some serious injuries or deaths over his lifetime as an instructor. Good for him. I'm thinking the seargent's knuckle approach was a little better. I'm wondering if OSHA would allow that for pointing nailguns around, like some of the lesser thinking construction hacks have been known to do from time to time. (Or so I'm told).