Since we don't know all the facts, and we're all jumping to conclusions anyway, I'll take one known fact and go off of that: the woman wasn't backboarded at the scene and was actually allowed to walk to the ambulance. If you know anything about EMS, you backboard a victim who fell and hit the ground, even if it's just suspected, and ask questions later, allowing a doctor to clear the C-spine. Since she wasn't, apparently she didn't fall. So then the driver probably didn't think he hit her and/or didn't think he hit her hard. And obviously with the minimal severity of the injuries, that proved to be the case.
Then again, I guess she COULD have had the only EMT in the world to not know that you backboard every suspected fall victim...