Bro banged on the door and broke a window to try to get in. He was literally forcefully entering a locked house, he didn’t just wander into an unlocked door by mistake.
No telling what the kid was trying to do or would have done if he got in. Home owners have to assume the person trying to kick in the door and breaking a window is there to do harm. Justified self defense to anyone with two brain cells to rub together.