Is that true? I wouldn't have thought so, at all, and a few minutes googling "do most concert pianists have huge hands" digs up a lot of sentences like "Plenty of world-class pianists have small hands, including Alicia de Larroccha and Vladimir Ashkenazy, and yet they seem to be able to cope with the most physically demanding works in the repertoire." And sites talking about how it's a misconception that classical pianists have or need huge hands.
Jazz pianist with huge hands here :-) Huge hands often goes with height, and I have never noticed classical pianists are unusually tall. I can't think of any who are. Maybe people are thinking of Rachmaninov (6 foot 6). One would expect classical pianists to look like towering basketball players if, as you say, they mostly have absolutely gigantic hands. But I'd say there are many more under 6 feet tall than over it.