Nit: the author says that supervised fine tuning is a type of RL, but it is not. RL is about delayed reward. Supervised fine tuning is not in any way about delayed reward.
Admittely most interesting cases do have delays.
In its most general, RL is about learning a policy (state -> action mapping). Which often requires inferring value, etc.
But copying a strong reference policy ... is still learning a policy. Whether by SFT or not