What Gman said. Boys have loved pretending to shoot each other since forever. Video games are just the modern version of that. An insignificant number ever bring it beyond pretend. Hell, now we have airsoft which is the most realistic to actual gun fighting we've seen yet. More so than video games. But we don't see a slew of airsofters out committing murder either.
The video this nut ball posted looked like a video game to people who saw it, but not to him. He wasn't living out a video game. The similar visuals were purely obvious to the viewer.