I agree with LarryJ, an immediate descent to 10,000 ft is likely a pressurization issue. Turning back is less urgent than descending, especially since they've got gobs of fuel on board they don't necessarily want to land with, and they've got checklists to run and ATC coordination to do.
Aviation Herald says the same, although I'm unclear if they had any source other than the same flight tracking data we're all looking at.