Cast is bend one way or the other; almost always, it's away from the shooter's face, no matter which side of the gun he stands on. Might be clearer if the terms were "cast right" instead of cast off; "cast left" instead of cast on--since a right hander typically needs bend to the right, and a lefty bend to the left.
I have seen some gun dealers make it clearer by saying "cast for a left-handed shooter".