Sorry to hear about your friend. Luckily it was not as bad as it could have been.
As a person that enjoys being functional below the waist, I have been warning against this type of carry for a long time.
The guy that lives across the street from me is an ex-LEO on disability from falling on a radio that had shifted around to the small of his back during a foot chase. It really does not take much to injure yourself in this manner.