I'm most definitely happy that you didn't draw on an 80 year old man who simply took a pistol out of a holster.
Simply put, I see absolutely no reason in what you have told here to justify it. I see no indication whatsoever of intent to harm, and I see no possible reason for you to have felt threatened. your remarks are that you never know, even 80 year old men sometimes barge into conversations and show their guns to people, and we need to remember that, so we won't be surprised.
you're telling us that the guy just walked up to you, drew his gun, and showed it to you. Not a word exchanged. are you sure that you didn't omit something? This story leaves me a little less than confident of a lot of things.