Thanks Ventuari for the info.
I can only guess at this point, but I've seen life-boat steel wire ropes snapping during tests due to poor condition, when the whole of the wire was oiled, but the part under plastic wraps rusted away...So I always suggest that the ropes close to ends are to be kept without this "protective" covering.
The other possibility is malfunction of the hoisting limit switch on the winch, ending in way too much strain on the wire rope (happenned on Anna Maersk, also with deadly consequences).
Since there are pictures of broken wire, I think that failure of the on-load release mechanism is out of the question.
I don't remember deadlier accident involving LSA training/drill.
RIP for the dead, I wish quick recovery for the injured.