A coworker told me that Muslims always wash before prayers and the coordinated bathroom trips would have reflected that if they all were going to pray at the same time.
No doubt they were passing notes so as to not disturb the Americans on board.
Waybackwhen, after 9/11, a couple of Orthodox Jews got in trouble with their fellow passengers by getting down on their knees on the plane and praying intently in a "strange" language (actually Hebrew).
I betcha' one of those musicians had one of those expensive Rolex watches that shows the call to prayer and the correct direction for praying no matter where you are in the world. Undoubtedly he was consulted by several of them more than once!