The episode, it seems to me, is a nontragic reminder that even responsible gun owners may not get mercy from gunmen who become unhinged when you have sex with their wives.
Lesson: Be a responsible penis owner too.
ADDED: This post is reacting to the way Think Progress goes for the anti-gun interpretation. I don't know exactly why the husband murdered the man he found with his wife. The two were not in flagrante.