In reply to Davidwi:
To me, it looks like the climber he passed did indeed move out from between the rope and the wall, probably thinking that the leader would have pulled the rope taught against the wall, with him caught in between, had he fallen, because that's what would normally happen had the leader placed any gear at all after traversing past.
Since the leader didn't place any gear, however, the result of a fall would be to take the loose climber off the ledge.