I'll say it's a Christmas Miracle. Oricon must have left out some figures somewhere, or there were a lot of end-of-week-only counts.
The first two days were supposed to total 18,778 (according to Oricon staff), so even if they made what 3rd place got each day, the total weekly would only be 31,832 (not including end of week figures, which would normally be ~2k) - and they were ranked pretty well below 3rd the rest of the week.
Don't get me wrong, I'm happy for them and all, but I just don't understand HOW the numbers and ranks are supposed to logically add up to 33,320 copies.