Thats what I thought at first too... look at it again. The vette was already angled towards the wall before the GT2 hit the brakes. For the vette to be headed at such a sharp angle it appears the Porsche bumped its rear as it was getting passed causing the vette to make a b-line for the wall.
Just watched it again, the gt2 definitely bumped his rear qaurter and helped him get squirley. Thats the kind of stuff I do to Paul on Forza