An officer would have to know you are armed to make such an order of assisting in a gunfight.
If I am unarmed and an officer tells me to assist in a gun fight, well you can guess what my answer would be to that
I have assisted an officer once I don't have my ltch yet and no law says i had to help (until the 2nd officer arrived) but feel i have a moral and civic responsibility to help. All i did was ask if he needed help he said yes and i helped restrain a guy when another cop showed up he cuffed him and told me to hold on to him. It would have been a lot more exciting if it was a gunfight but it still made a good story to tell in criminal justice.
Nor does anyone want your help.
The one I will always remember was attempting to get a meth head under control on the side of I-74 at 0300 hrs. Felony burg warrants, stolen truck ect. This guy was wired and a big boy. Tazer didn't connect, lost it and then it got kicked into the road. I was honestly getting ready to go to the gun. I heard tires locking up and next thing I had some truck drivers all around me with tire irons. They wore that boy out needless to say and even cuffed him up for me. I will admit I was out of juice and didn't have much left. It made me rethink a whole lot of things. I am forever grateful to those truck drivers.
There's certainly no legal responsibility.
Moral responsibility? I don't personally think so.
You both probably have a driver's license-- does he want you to get involved in car chases too?