He'd only have to misjudge it by an inch to end up like this, I think. If he were trying to jump in front of the train at the last moment, but missed by an inch, he'd bounce back and send his legs flailing into/under the train.
I've been on vehicle accidents where people have had arms or legs pinched off with very little bleeding from the artery's being sucked in and pinched off by muscles, only some times.