The driver should be spending some time in jail.
Even though the crowd was shouting flip the car? Someone opened the rear door (where his kids were) too.
I agreed with you until I read about what happened and am now on the fence.
A couple of years ago, I showed up late at my tailgating spot for our biggest rivalry game. My vehicle was absolutely surrounded by boisterous, drunken students, a few of whom knocked on the doors and windows (my wife and kids were with me as well). It was obviously just a case of students being students. Nobody was in any danger, unless I decided to do something stupid like blow through the crowd in my vehicle.
The zombie walkers should have used better judgment and shouldn't have blocked traffic. But the correct response by the driver is not "run a bunch of people over." If the driver honestly thought that he and his family were in danger of being consumed by zombies, he's not qualified to have a driver's license.