For what its worth, the only plausible explanation I can come up with is if the window was partially up, even a little bit and a rock from whatever, a dump truck or something hit it hard. This would cause the entire window to explode due to it being tempered glass.
This is why windshields are not tempered. A rock that would normally chip your windshield would cause the entire thing to explode into tiny bits, and that would suck.
However, this does not make the car a POS or have any effect on the status of the car and isn't worth all of the drama. That and I still think your brother did it.