I can't say for sure, but a photo I saw that was taken after the accident might be a clue. There's no tire on the right rear rim of the Porsche.
http://fourtitude.com/emAlbum/albums...o-Audi-305.jpg
Whether that was a cause or effect, I don't know, but there's no evidence of there being a tire on that wheel, and there's significant damage to the rim, too.