Guessing it was in a state that allows full-auto.
I don't think this matters at all. Since 1986 there are no more full auto's being alowed in private hands, ala Federal regulations. This AR was made long after 1986. To be legal, outside of the military or police, it is way to new. Only Colt made guns of the AR type were availible pre 1986...
I suppose TR's exemption could apply, but I am not aware of that.. States rights rarely trump Federal reg's though..
There is a very finite supply of private class III guns. No more are being alowed, ever.... Hence the price of an M16 is around $15K or more.
Unless these guys are law enforcement officers, and I doubt they are cooking bacon on a barrel, I think they could see time in club fed for this You Tube....
Regards, Kirk