It sounds like he made up his mind to retire. I dont think he wants to fight Hendricks again. Unless this is a clever way to announce a REMATCH to fight Hendricks again and build up some suspense right from the bat. If that is the case i'm wrong in saying he does not want to fight Hendricks again (Obviously lol).
I know people are talking about GSP not performing the way he used to and its most likely a mental thing. But i personally never agreed with that. I think GSP is performing the same way and his speed is still there. The first 3 takedowns versus Hendricks in the first round were amazingly quick. He was able to catch Hendricks off guard with it and took him down fast. The next 2 Hendricks knew was coming and stuffed it with a planned upper cut. But those Takedowns were prime GSP takedowns. He also threw the inside lead leg kick faster then iv seen anyone throw. He was in and out before Hendricks could throw a punch.
Iv never seen all this slowing down and "that obviously wasnt the GSP we know from a few fights ago" that other people talk about. I think the only thing that has changed is that he is facing better competition and thus he cant look as good. He would still beat all his opponents back to his first fight very handily. The only opponent he would not beat is Hendricks. And thats the opponent he is getting.
This is a good time to retire. He has the belt, the record, the money, the fame, respect, etc etc. He has alot to lose if he keeps fighting and from GSPs interviews its obvious he cares about leaving a superb legacy. Which IMO would be good even if he rematches Hendricks and loses but im sure to him retiring with the belt is alot better and easier then retiring on a win streak breaking loss and no belt. Especially when then people will say "Well he should have 2 losses in a row right now". On the other hand currently you have some people who believe GSP won the first fight fair and square (Im not one of them mind you but what i think does not matter since GSP has that W).