So should the old guy have answered the door with a gun in his hand or not? From the article:

Doug Harbord, who lives nearby, said he can't imagine how his friend could be considered threatening.

"If someone is banging on your door, making a bunch of noise that you're not expecting, out where we're at, I would go to the door with a shotgun in my hands ... even if they yelled 'police,'" Harbord said. "I don't know all the circumstances, but from what I know of Bert, I don't think he was a dangerous individual." 

If you are serious about the right to bear arms and expect to have to defend yourself, you can only come to the conclusion that this guy did what was to be expected. The police should have known that this guy might would feel threatened by loud banging at 10:30 at night, and had themselves in a position where they could protect themselves until the situation was diffused. They are the professionals. They are responsible for the way the events unfolded.