Somebody asked on another forum what the slow-mo guy did wrong. It's hard to tell from the camera angle, but it looked to me like the RO was saying he swept himself with the gun, maybe his hand. Not a huge deal with Airsoft, but still against the rules if it's an IPSC event. I'm not sure what they're actually shooting there, either--if it's Airsoft, it sounds like it's spitting metal balls and popping them out pretty hard, from the ringing on the steel plates.
I suppose these guys see this as no different than playing kendo on the weekend in a country where you can't own a sword, either, unless it costs more than my car.