Neither of you is properly reading what I wrote.
Obviously, I know that the ball becomes OOB when it contacts the back of the backboard.
I stated that the backboard is LOCATED inbounds. Thus a thrower would have to pass the ball such that it breaks the inbounds plane in order for it to contact the backboard. That is why the thrower can't do it.
On the other hand the thrower may cause the ball to strike other objects which are OOB such as the floor, the wall, the stanchion, a chair, a table, etc., as long as the ball remains on the OOB side of the boundary plane and does not carom into the court.
Do you now grasp what I wrote?
Since the front face of the backboard is positioned four feet from the vertical plane of the endline it would have to be an excessively thick backboard to have part of it located OOB!