I imagine they may have had an overnight on the day before, like landing at 0600LT for example, then proceeding to sleep immediately, waking up at 15, walking around, then trying to get a sleep before being driven to MUC. Body cycles pretty much stressed at that point. Then again it's just pure speculation, don't know how AB's Crew Planning is handling this type of things. Those actually happen a lot I suppose, they just usually stay in company VR's...