Because you saw the gun and wisely deescalated the situation. Had you not seen the gun, that situation could have gone any number of different ways that wouldn't have ended with you going home. You both got out of your cars. That's called mutual combat. Different states view mutual combat differently but, generally, it complicates your legal defense and likely makes it an unwinnable defense. If you killed him, your life would have been over as surely as his I think. It's a good story though IMO and worth discussing and contemplating.
I have been in a similar situation. I was carrying a J frame .357 concealed. I didn't know if they were carrying but I knew there were two of them and one of me and they were having words with me over their perception that I had cut in front of them in line at a shoe store of all places. This was back when the pandemic first started and everybody was supposed to stand 6 feet apart on the little dots as they checked out. I wasn't able to both stand 6 feet apart and on the dot and this stupid little dot on the floor almost led to two young heavily tattooed billy badaxes following me out into the parking lot. Had they done so, I would have almost certainly pulled that .357 and if I pulled it out, I would have shot at least one of them and then I would have ended up in court having to explain to a jury how I killed one or two men over a dot on the floor. I saw how bad this could end up and deescalated that situation and it was pretty tense. I mean, the store was full of people and words were being openly exchanged and individuals in the crowd were involving themselves in the matter. It would have been bad. I ultimately looked at both of these guys and told them in front of a dozen witnesses and on the store's camera "look, I'm trying to walk away here but you're the ones not letting this go". I think maybe the hint was taken as they didn't follow me out the door although they continued their verbal assault. I think maybe it would have been a lot less drama if I was just openly carrying a full sized Glock that day.
So, you're saying that by seeing the gun, you deescalated the conflict. From my perspective, that is what allowed everyone to go home that day. I prefer concealed carry but, at the same time, I understand the old saying "a well armed society is a polite society". People are less likely to escalate a situation if they know that it's going to lead to someone getting shot. Again, I prefer concealed carry but I can't deny that there is a reasonableness to open carrying instead.