How does something like this happen?

 
It took place on Friday in Kentucky and is anyone's worst nightmare. A 7-year-old girl was dragged 1,000 feet down a city street by a school bus after her backpack got stuck in the door.

The unidentified girl sustained badly skinned legs, but things could have been a lot worse if it wasn't for the red car in the video. Watch as the Camaro jumps the curb to stop the school bus.

My only question here is how does the school bus driver not see this happening?