Guns almost never go off unintentionally. Yes, people think the gun is unloaded, or toddlers are playing with the gun, or the person with the gun is being unsafe. But the vast majority of the time, somebody pulled the trigger. They are not accidents.
Since they were "line hunting", pretty much every hunter thought Cheney should have been charged with something. In Canada, he definitely would have been charged with unsafe usage of a firearm.