From what I heard this morning, the truck was actually stopped as the person in the wheelchair passed in front of the truck. Not able to see him since he was so close to the front grille, the driver started moving forward nudging the wheelchair so it ended up turning forward and getting stuck.
Lucky it turned forward so the wheels could turn. It stripped the rubber off the tires, but if it had been sideways, it would have probably collapsed and gone under the truck instead.
I believe it was a Bill Cosby stand-up routine about the way mothers always tell their kids to wear clean underwear in case they end up in the hospital. He said that it was impossible, because as you realized you're heading into the accident, "First you say it, and then you do it."