aswanson has the right interpretation. Wilson is in an SUV, so he's sitting up near Browns upper torso/neck/head. It's pretty easy to manipulate someone from the back of your neck...those muscles aren't really strong...and Wilson is also the same size as Brown. So it's not hard to see wilson reaching out, grabbing Brown by the neck, and pulling his head in through the window. Especially if Brown was taken by surprise.

I didn't mean he pulled his whole body in through the window. That would be very difficult to do!