It depends what clipless pedals you are using. My friend hit a football sized pinecone during a sprint, and because he was using speedplays (harder than most pedals to clip in/out), he flipped over on his back still attached to his bike. I however atm, use m520s, a friend on my left side made a right turn into me; I some how clipped out of my pedals and landed on my feet.
I would say "... because he wasn't looking where he was going, he flipped over on his back ..."