Rule One: The Doctor lies.
Rule Two: People other than the Doctor Lie.
Personally, I DO think it is a later incarnation of the Doctor who has become the Curator and is having a moment with Eleven. Behind the scenes, he was helping the plan move forward.
I do not believe the Curator is an alternate, aged version of Four. I don't think he is a very well-informed 'someone' pretending to be the Doctor, either. BUT-- I do feel there is leeway in the presentation for others to interpret things differently- and I am willing to leave it open to the individual to choose. That is what they say about a lot of artwork, isn't it? The interpretation is left up to the viewer.