Thanks for the information, Ard. I hope my X5 doesn't repeat what your lemon did! I will document each anomaly from here on out. Happily there have been none.
When I think about the circumstances around the appearance of the light, it was also during a period when I was doing many short trips. Which points again to the regen.
The SA was really attentive and even gave me a free quart of oil in the snazzy BMW zipper pouch. I will review the paperwork to see if my mention of the check engine light was documented. Good stuff on this forum!