I will second anonsy's sentiments. I would hope he'd be less Bill Clinton-esque in his approach to answering questions 'honestly.' But maybe he now thinks that this 'truth through strict definition' is the only way to protect his privacy/ image.
Also, IF it is true and she was in London with him - girl is playing the long game (and tallying up some major air miles while doing it). And she has to, because you don't want to have thrown over your fiancé for a guy who only sees/wants to see you once a month. As has been said here: she always rocks up to TH, never the opposite. And for this sighting, TH traveling in the opposite direction would seem more logical. We know he's going to Oz soon, probably via LAX. So, wouldn't it seem easier/more convenient for him to fly out to her in LA, celebrate NYE there, stay, spend some quality 'door time' together, and then head off to Oz? And, no, I don't think she made that journey for a special reason (long stay, meet the parents, proposal, etc.).
And it wouldn't surprise me one bit if she showed up in Oz. She seems perfectly willing to get on a plane for two things: fashion shows and TH. (Sarcastic/unfair remark: But not to end an engagement.)