(Update 6/30):
She's back in my garage. It sat in the lot all week and I have no more answers today then I had then. That's right. Nothing was diagnosed and I have the car back after they were kind enough to reset the check engine light.
I have no explanation from BMW NA or from the dealership. They couldn't recreate the problem. They told me to bring it back if it happens again. The only theory is maybe there is something wrong with by charge cable which I plug into a standard 110V outlet. If I get the light again, they want me to also bring in the cable.
Not very reassuring, but the car is behaving fine.
