Yep - Sydney has a population well in excess of 2 million. As you say, a lot of them don't celebrate Christmas, there are often travellers on holidays visiting Sydney, and pretty-well everything else is closed on Xmas Day.
20 years ago there would only be 200-500 people in total for the whole day. Some time during the 90's word spread and more and more people started visiting.

Hix
20 years ago there would only be 200-500 people in total for the whole day. Some time during the 90's word spread and more and more people started visiting.
Hix