The situation was definitely handled very poorly and the "vigilantes" definitely went overboard. I think it was a good idea of them to go check the situation out and confront the people, but they did it completely wrong. Before they saw the people the legitimately thought that the people may have been robbers, and robbers carry weapons, so carrying a smaller weapon would have still been acceptable. But whenever the victims provided a logical explanation, the vigilantes should have backed off and apologized. Even if they were robbers with some huge masterplan (I'm giving the "vigilantes" the benefit of the doubt in saying this was what they thought) they should have let the victims go. I mean if these "vigilantes" true concern was the house getting robbed then they would have realized that the victims (who they thought to be robbers) would obviously not rob that house anymore. It would be much to risky after being stopped.
This is how it should have went down:
Best thing thing to have done: Call the cops...nuff said.
acceptable thing to do: Approach the suspected robbers armed with a pistol. Don't put the pistol to their heads, just have it in case it turns out to legitimately be robbers. Then ask them who they are and what they are doing. When they tell you their story, but don't have papers, tell them that you are very sorry for scaring them. If you wanted you could politely request they come back in the morning with the proper papers. That would still be improper, but much better and more acceptable than what went down.