here's a classic "my friend said" to add to the rumor mill. She heard it from her friend in YOSAR.
Supposedly, the route he was rapping overhung, so he had the end of the rope anchored to the next station, forming a "J" in the rope. he rapped to the bottom of the "J" and was batman-ing up the (static) rope, when he fell before clipping in with the sling to the anchor. the resulting shockload blew his belay loop apart.
let's see if that's what ANAM publishes.