It may depend upon how someone calculates "over Christmas."
We were at WDW for a week that led to a Friday Christmas. Not much was crowded at all until Christmas Eve Day afternoon. And that was MK. Epcot and DHS weren't any more crowded than we'd seen in mid-November in prior years.
From what I've heard, from Christmas to New Year's Day is ridiculously busy. If that's the time referenced, I agree that it would seem unlikely any reasonable person would agree that's not a popular time.