It wasn't necessarily the video game that killed him.
Doctors reportedly suspect deep vein thrombosis. That's when a blood clot forms in a deep vein, usually in a leg. This can happen if you don't move for a long time, which the teen hadn't done. The blood clot can break loose and cause death.
Even without the broken leg, investigators said evidence indicated the teen had most likely been playing the video game for nearly 2,000 hours over the previous year and a half.