I think he means New Years Eve in NYC is already 1/1 (day late) in Australia.
Got it, missed the Ny in his post, though that doesn't make it any more well worded. Maybe 'Especially with it already being New Year's day for them' would have worked a little better.
I realize it was in jest at the fact that aussiebochur started this thread, but I can't imagine it has such a big viewership outside of the US. I always assumed it was more of an American tradition, if even that.