Of course the anniversary show was fanfic! It wasn't meant to be a super spooky or affecting episode or anything, it was meant to be a fun zany romp! Like I'm usually disappointed by Who because it could be so much more than it is, but this is one episode where it's perfectly acceptable to be just pure fan appealing silliness.

Also the Doctor thought he couldn't go to Gallifrey because he lost all memory of what happened in this episode. As far as he knew it was destroyed, but it never was. It's not that it was previously destroyed but saved in this episode, it was never destroyed in the first place, we and the Doctor just never knew that.