It's really unfair to compare offset and frontal crash tests. You can't draw any conclusions by comparing the two. For years, auto manufacturers were able to perform competently in the frontal crash test, but when the offset test was introduced, the failure rate went through the roof.
I don't mean to diminish the performance of the Tesla Model S. It is, without qualification, an incredible car. I just don't think comparing it to the offset video of a BMW are relevant.
It sounds like it's a special band running around the car, made of multiple layers of aluminum with space in between each layer. The layers crumple and transfer impact across the side of the car like a ski resting on soft snow.
A bmw 3 series (not full frontal): http://www.youtube.com/watch?v=4XG8BQt4sHY