My last thought is that the sky-box is actually a rotating hemisphere with dynamic cloud creation (just like what milk said) and the sun is moving on arc-shaped path (if you consider the shadow of the car that revolves around it, you may be agree with me). So at that specific moment the cloud and sun are rotating/moving alongside each other in the same direction, so shadows are going from right to left (compered to the clouds) and toward the car.
You can watch this video which the sun position is perpendicular to the clouds and the shadows are moving in the direction of the clouds (from 2:30 to 3:10).
Clouds move in a circular manner while shadows move on a straight line? The sky is completely filled with clouds while cloud shadows appear sporadic? Something doesnt add up