Dropped my C-Max off at the Ford dealer this morning and explained what happened. The service advisor called later to say that the engineer he talked to explained that the only way the fan motor would come on is if the car was on -- no way it would come on in Acc mode. It's certainly possible that I could have left it on, forgetting to power off then back into Acc mode. I forgot to mention to him that only 12 miles were added to the odometer, so there's still a bit of a mystery there.
I do have the remote start feature. The key fob was in the lower pocket of my cargo shorts, and it's not easy to double-click the button to activate it, but I can't rule that possibility out 100%.
I'll update again if I learn anything new. If anyone has any other theories or their own experiences, please share.