At some point the NBA needs to look at the hand going up from the person going for a layup foul. So many guys see someone about to crash into them so defend themselves with the off hand to protect themselves but get called with the offensive foul. That Smart foul was exactly that.
If you use the are to create space. Offensive foul. But if you're using it to protect yourself from an incoming hard foul, that should be a shooting foul.