Arafah Day changed by the Saudis?

I don't get this.
How can Saudi change the day for Arafah/Hajj. Apparently, it's pulled back by a day.

They supposedly made a mistake? what's really going on? Our Eid Al-Adha is a day earlier so tomorrow is going to be the 4th Jan too according to Saudis?

What's really going on? I can't find anything online to confirm this.