I was standing about 20 meters away, and that other report sounds accurate to me. I saw him in the chase pack, looking fine, then all of a sudden he stumbled, grimaced, hopped, and fell. Then someone tried to drag him off the course and several people yelled, "Don't touch him!" I guess it was quickly obvious that he wasn't going to get up and start running again, so some people dragged him off the course.
I don't know if he got spiked, but I would guess not. I didn't see any blood, and I don't think anybody could have been able to tell.