No, it's both and more often than not it's around the 25th of December since the 7th of January pretty much everyone gets back to work (the 7th is typically a holiday for kids so they can play with their toys, but kids aren't getting festival tickets as a present) and it's common to get holidays the entire last week of December and gather with the family then.
However a bit chunk of the public (~40%) is international, so it's certainly something to keep in mind, added to the fact that other festivals (Primavera Sound, Werchter...) are selling out, so many might have ruled out Mad Cool in favour of those fearing they could miss out.
And I am with Big Kahuna here, many are waiting for Mad Cool since other lineups have been rather disappointing, so there's still a big piece of the cake. If they deliver they will do well; if not, good luck, hardly anyone is choosing Mad Cool above other festivals/plans if there's an alternative.