BBM: I am only going by the location I have seen marked on a map, and descriptions of the area, but there are two roads there, and a hill between the top road to the bottom road, so a vehicle on the top of that hill could easily be rolled down the hill. But that's when I have to wonder about the back window being broken out. It is obvious when a window is broken from the inside or the outside. LE said the window was broken with an emergency tool (it's pretty distinctive when you use one, the safety glass breaks in a specific way) and if it had been broken from the outside, I would think they'd have said so. If it was broken from the inside, the glass would then be outside the vehicle, and if it wasn't in the right place next to the vehicle, that would also be a clue and most likely noted. Assuming the glass was in the right place, it's hard to imagine someone climbing in the upside door, crawling through the vehicle, and breaking the back glass to make everything look right.
My guess is that if Bryce (or even anyone else) did roll the vehicle down the hill on purpose, he didn't expect it to flip. That would be luck of the draw (hit a rock just right, over steer, contact with the lower road just right, car going down at the wrong angle, etc).
ETA: it just occurred to me that someone COULD have broken the window (my experience is that it shatters, but doesn't break apart until you hit it again), but left it in place, then crashed the vehicle and the back window came out. It COULD happen.