He is talking about being released to rest (or in this case to home since it is the last day). At SWA you have to call and ask to be released unless you are on the last day and meet certain criteria.
Unlike most carriers, when you are given an assignment, you aren't treated like a lineholder. You are still responsible for being available at RAP start and they can contact you and change your assignment any time. Once you are done with the assignment, you have to call and ask to be released. Theoretically they could put more flying on you. In practice, they will do that via crew web anyway, so the call isn't necessary, but it's still in the contract.