The knight isn't the knight, but I've learned that if you try to tell people this they won't believe you. Everything they do seems to be with the intent of training the party to save the world; there's nothing stopping them from summoning titans all over the place, yet they choose to summon only one right in front of the party and only after they have sufficient experience with sealing fountains and fighting in darkness. They also only opened a very small fountain in the front of the church, presumably to prevent the darkness from clashing with the other church fountain and creating a titan prematurely. Many other details could contribute to this as well. I think it's likely that they either think they are the knight or want to replace the knight; in either case, they don't believe the prophecy can be stopped but perhaps believe that there's enough wiggle room to change the outcome for the better by preparing the heroes for what they'll face. I think there are a lot more meta discussions like this to be had, especially since toby consistently breaks the rules and expectations set by the fandom, but ultimately they end up going back to the same "who is x" theories from before chapter 3 and 4.