I would agree with Nik there, it is most likely the adrenaline running through his body, when I was young, I used to cycle to school, I got hit by a car went over the roof, and the car and smacked the floor pretty hard. I broke my arm badly in both places.
I was more worried about meeting my brother, as he needed to be picked up from school, with the broken arm I wrenched my bike from under the car, and was screaming mad at the driver, no pain at that time, until the paramedics sat me down, and a few minutes later I nearly passed out, when they got my mum on the phone and they said my brother was picked up by my aunt.
Your body does wondrous things to suppress the pain, same as when I chopped the top of my thumb off in a door, and didn't feel no pain, and wondered why all my class were screaming, till I look at my thumb on the floor lol, and then the pain hit.