I have worked with bystanders ("zombies") in a variety of emergencies with positive results. In general, people are willing to help, especially if there is direction and guidance.

On one climbing trip, my partner and I recruited and trained a group of strangers to the point that we were able to convey a victim, loaded into a Stokes basket, about 500 feet down a steep slope, all in about 45 minutes.

I have been impressed at how quickly nurses respond to unexpected emergencies, with great competence. That is probably why, in my younger days, I frequently dated nurses or RNs in training. Safety First!!

It is oversimplifying to divide the universe into preppers and zombies. There are many intergradations and variations. A lot depends on the situation and the specific situation.