I would continue to pursue with BMW , Although this wasn't my situation I have had the experience of a dealership telling me something utterly ridiculous,
a couple years ago I replaced the stock stereo with a aftermarket piece fold out display etc.
Then I got an error with my steering wheel column. they proceeded to tell my stock stereo needed to be removed. Went to the audio guy who is a good friend of my dad and he said no way that's possible its the silliest thing I have ever heard.
The dealership wouldn't budge and I had to pay to have my radio switched and then sell the old one. (now I actually could do this myself probably it wouldn't have been as big as a pain )
but then when I moved up to Boston for college I was in a service center there and found out how idiotic the service at my local dealership is and they couldnt even understand how they came up with that, and they were been lazy ,
sorry im bitching about this still hahaha but my point is unfortunately not all employees will have the same knowledge set or work ethic. some mistakes may be innocent and this may be one of those cases where they didn't know. good luck id be so nervous driving that thing with your story