THat story is a good reason why parents must supervise their children until they leave home, so kids can be kids, and mutilate or kill themselves with their mistakes. It takes a lot of time and practice to learn safety habits so they are practiced without effort about the same as breathing. Give your kids that time. Don't let them go hunting or shooting without you being there to supervise, and catch their mistakes. When it comes to gun safety, that is the time to be a NAG!
I know of an incident where two boys were taught to handle safely a rifle and shotgun respectively, but were not taught both. The next day, without supervision, they sneaked off to go squirrel hunting. They switched guns. The 12 year old slipped and fell, and fired the 20 ga. shotgun into the back of the 11 year old. He died almost instantly. His finger was on the trigger, the safety was off because he didn't know how to put it on, they had no training in hunting, or safe gun handling- the list just grew and grew. It was an accident that should never have happened. The one you describe is another one that should never have happened.