No way.
There is NO WAY a truck ran over his HEAD, and all he got was a concussion. No helmet is THAT tough.
He either got a glancing blow - which granted, a glancing blow from a truck can be pretty intense - or the truck bounced over a curb and rode over his head. Regardless, no styrofoam and plastic helmet is going to hold up under a truck. There is too much squishy stuff underneath (i.e., his head) for that to happen.
That is not to say, of course, that the story wouldn't have had a radically different ending if he weren't wearing his helmet, and he's danged lucky. So, yeah, always wear your helmet.