Originally posted by Madzilla:
It looks like that article came out before S2 started, so that means they're referring to the teaser ads with the ballet costumes (which weren't in any episodes, as they say) and the matching publicity pictures for S2 - which of course Mac is in as he's been in the series so far. Doesn't make anything certain for the Xmas ep though.

I think he'll be in it, but I don't have anything to back me up, I'm just going by gut instinct.