UPDATE: The engine malfunction warning light came on Saturday night. Didn't drive the car Sunday. Just got back from a drive and the car ran fine, no warning light. The warning light also had disappeared that Saturday night after our last stop.
Called Beverly Hills BMW and spoke to a service adviser. He recommended a 'wait and see' approach and I am fine with that. I didn't really follow his explanation of what might cause a momentary "glitch" that produced that message without any real reason. But we'll see. It may never reappear, it may reappear soon or way down the line. I'd rather it not have happened but I am not going to let it spoil my enjoyment of the X1...for now!