I wasn't present when this happened, but looking at the photos, it seems to be a fall while descending Sea Gully. Although this is relatively easy by today's standards, with most climbers soloing down it, there aren't many positive handholds, so a slip can have major consequences. There is a good thread at the top of the gully, which can be used for lowering/abseiling. Worth considering if you are climbing down that end of the crag.
If at all wet (which it usually is) a 30 metre rope will see you down. It is possible to leave a sling and carabiner in the thread and use a doubled climbing rope and pull it afterwards. The sling can be collected after any routes have been climbed. I hope that there are no serious injuries and that quick recoveries are made. All of the descents at Bosigran have serious sections and conditions and the experience of the party should be taken into account when choosing which is best. If in doubt it is perhaps wise to walk around to beyond the Alison rib area and descend easily there.