Since the two clearly were convinced they were right ("don't bother me with the facts. My mind's made up.) the only way you might have made them doubt their position would be to give them some bit of official literature that might have caused them to go home and investigate this on their own, then realize they were wrong. They wouldn't ever want to admit that publicly when talking to you. I usually carry copies of the letters from the VCDL website regarding open carry in restaurants. They are on State Police letterheads. You can print them out and keep copies with you to show people who refuse to accept your verbal arguments.
You're new to OC, so you will find out how frustrating it can be to deal with hard-headed, opinionated people. Nonetheless, we have made progress over the last few years educating people about the legality of all of this. I can't tell you how many friends, neighbors and co-workers get this amazed look on their faces when I tell them about the legality of OC, and especially of the NECCESITY of OC'ing if in a restaurant that serves alcohol. ("No way !! You actually have to do that to be legal??!! That's really allowed in Virginia??" "Yup")