@macroblitz &
@riflow
To frame my response, I am from the American South, and have hillfolk and mountain folk as relatives, friends and acquaintances.
In a town/village that has hunting and gathering as an important or even primary way of getting food, guns are treated much differently than in urban, suburban, or even normal rural areas. A rifle is basically an extension of one's self, so they are used more blatantly than in other environments. If someone goes onto private property, or tries to intervene in a family dispute, a reaction like the grandpa showed is not unexpected, even today.
To make matters worse, the clannish attitude of the grandpa (for similar reasons), such as the obsession with traditions, and violent distrust of outsiders, can be very common. Kids adopt their parents' prejudices at a very young age, and it becomes self perpetuating.
Law enforcement has to be very careful in these areas, as they are so isolated and clannish as to be little different from the way they were in the 1850s. There are still areas in the Catskills and Appalachia that don't have electricity and running water. They are ever more rare, but still around. Law enforcement either has to tread lightly, or risk death for properly performing their duties in a fashion that is common anywhere else. Some family "hollers," valleys lived in by generations of the same family, are basically off limits to everyone, and law enforcement ignores everything except blatant murder.
For a Japanese comic, I was surprised at how familiar the attitudes and behaviors of the people in this story were to me. Even down to the "authorities" backing off from offenses that would have gotten prison time in a normal town, for the sake of "keeping the peace."