In your case it seemed to be a good thing that the guy (with the gun) didn't react in time.
Some people just... I dunno... don't have the wherewithal to mentally be responsible enough to own a gun. This guy was going to SHOOT you simply because you're walking up to his car... sheesh.
Having a weapon deployed and ready is not the same is shooting or pulling the trigger. It could be is natural reaction to seeing a 6'3" 280 (* I think that was my weight then *) guy jump out of a car and raise his hands start to approach, when he was just stuck in traffic.
Now, while talking to his wife (* we all talk in cars with other people *) he did not see in his mirror the person behind him.
I always watch my mirrors. I have been rear ended before and when I come to a stop I watch those behind me. Even more than one car as there can be a multi-car accident. I have had people get out of their car and approach my vehicle before. Both from the front and behind. (* Location Location Location.

*)
So, being the well trained person who has learned from their mistakes or as some might say the slightly paranoid individual I am I always look for trouble.
So in the original case the guy is pushed out of the way, and he is surprised by it. Like I said the guy would not have gotten that close to me and would not have touched me without being touched back.
In my case the guy with the gun was surprised it happens to everyone, but the guy who swung on could have gone after the guy with the gun. What would have happened then instead of me just passing his strike and checking his shoulder so he fell? With the guy with the minivan and his wife and kids in the car, I could see where he would be afraid for life and family life.
In another case, I was ready to turn right and there was just enough room to do so and then stop and wait for the light on the next street, when the light turns green for me and I begin my turn. The guy across form me who had the left already runs his light red (* Note my light was already green *) and he barrels out across me flips me off and blows his horn and cuts me off. I stopped my car and flip him off. (* I know bad reaction. I was younger and I make mistakes what can I say *) He then reached into the back of his car and started to look for something while yelling at me through his open passenger window. I was thinking gun. Yo get one or two or three pointed at you and do not want to be trapped again. So, I put the car in reverse and try to back up. The guy behind me sees the reverse lights and backs up so I do not hit him and so forth until I get about 25 feet. Then I realize I can get out and run, but not real cover, only concealment. So I drop the car into Low 1 and rev up the engine to while brake torque is holding the vehicle in place. Most guys have done this before. I was ready to launch my vehicle at him to hit him if a gun came up on line. I figured if I hit him hard enough maybe he could not shoot others.
Note: The Passenger which looked to be his wife, which I have not mentioned until now was already dead in my mind. This guy had given up this person's right to live with his possible threat. I was willing to turn my vehicle into a weapon and most likely kill some one. (* His car was a little Ford Escort and I had Pontiac Grand Am. Just enough mass to that she should have been crushed. *)
The guy finally comes up with a Mag Flash light and shake it at me. I take my foot off the pedal and begin to laugh. The threat was not as bad as I thought it could be based upon previous experience. This guy just continued to yell and shake is flash light at me. I just waved at him and let the guys behind me honk their horns while I watched the other cars pile up behind him before he moved on. Once he was clear, I turned right and continued my with my life.
The point I am trying to make, is that I would not have let him have kept the gun on line. I had plans to drop the seat back and fall back to reduce my target window on me. As it was a straight shot I did not have to worry about my aim with my weapon. I would not have let him get out of the vehicle as I would have launched the car at him and his wife.
What I have found. Most people are not ready for this situation. They are surprised or the adrenaline gets them or the panic or flight versus fight. (* there is nothing wrong with running away to avoid a conflict to live another day. *) But is you are trapped and unable to move out then what does one do? I have also found that when it comes right down to it most people do not have it in them to make that decision to take the person out. Be it temporary or permanently. Some can do it in a fit of rage, but then it is an accident not something the react too and choose to do. Hence my comments about poking the guy and then locking him up and dragging him off as my plan and usually is my plan, unless I am backed into a corner with my life on the line.