What exactly makes you think you will notice if it's a prototype or not? Some prototypes are very close to the finished car, not everything is some concept car or alpha version. A prototype can even include many components that are 1:1 the same as in final production even manufactured on the same machines.I sat in that selfsame car during the press days - it had nothing of a prototype to me. It couldn't have been either, what with the wringer it was put through by visitors to the Tesla booth. And yes, in German Mr. BMW's declaration came across as rather dismissive.
According to the German Forum it's a Founder edition car and there have already been several discussion on this forum where people think those cars were to a huge extent "handmade" and not utilizing the production line with the robots to the full extent. So while it might not be officially a prototype the production could have been closer prototype production than to serial production.
Autosalon Genf: BMW checkt Tesla Freunde