Dude, he's the Ultimate Impostor, he impersonates people, in DR2 it's said that he impersonated so many people that there's a possibility he doesn't remember who he was
The Ultimate Animator is somebody who's already known by the time this Arc begins, so the Ultimate Impostor he decided to impersonate the Ultimate Animator
Also the FF doesn't exist in the Despair Arc timeline, the fact that he's impersonating as somebody who is going to be in the FF is purely coincidence, same as when he impersonated as Byakuya, he didn't know they were going to be members of the Future Foundation, he just knows how to impersonate them
People are looking too much into this, when this is as straightforward as it can be, same goes with the blood being treated like a clue when it's stylistic choices