Young found a way to create contact and get to the line. It's not like the move is new. It's happened throughout the history of the game. But for a fast guy that can get past defenders and stop on a dime to force the contact if the defender is following him, it can be weaponized, which is what Young has done.
Good for him!
That's off the charts BBIQ if you ask me. It's like Stevens using players, often that are moving, like a lineman, in football, for the running back to follow. It's legal and been in basketball a long time, but not utilized as a weapon like the Celtics do. It's within the rules innovation.