I suspect he was over-reacting because of his lack of ability to maintain situational awareness while riding.

I'll go next. Today I was toodling along with my wife. As we approached a stop sign another rider passed us. He proceeded to run the stop sign and begin to turn right without looking in either direction. Fortunately, the motorist who was coming from his left was paying attention; she stopped before impact. Part of the reason the motorist was able to avoid running the cyclist over is that she was preparing to park just past the intersection so she had slowed down considerably.

Now, both the road we were on and the one that the cyclist was turning onto are very low traffic roads. It is quite rare to encounter another vehicle there. However, that is no excuse for just assuming there will never be anyone coming. I really think it is a good idea to stop at stop signs, but one should at least check for traffic that has the right-of-way before running them.