There are only 807 undergrads[1] at Harvey Mudd (which of course is an excellent school).
So that's still a sizable portion of their undergrad students -- even though from such a small sample, it's very hard to tell whether what they are doing would scale.
Also worth noting -- Harvey Mudd is focused on Science and Engineering, so students who pick HM would likely be more predisposed to picking a major like CS, anyway.
But still, an increase is an increase, and they're not out of line to cite those numbers, IMO, they're accurate.