one programme would certainly have put the kibosh on the other. But it isn't Newsnight's job to promote other department's Xmas specials. My guess is you're right, it was pulled to save face. But I don't think it's at all clear how this was done and who was ultimately responsible.
Incidentally, a good piece of trawling at the beginning of your Q. Now that everyone's saying "Of course, I knew this all along, everyone did" it's worth remembering that no, everyone didn't know. (I didn't, for a start.)