Wow, that's a shame.
I've learned to try to see things from other's perspective and give them the benefit of the doubt first. We all know how emotions can cloud reason. Maybe he or a close friend or relative was recently involved in a shooting?
Some people's gut reaction is to blame anything involved in a traumatic experience (like cars with a car wreck, etc.). Who knows what his deal was! But it sounds like you handled it very well.
One never knows what is going on in another person's head and stories like this certainly reveal that!
I'm glad it hasn't changed your mind about openly carrying. Hopefully your soon coming next experience will be much better!