Ah, I think that was to distinguish between applicants from China and those ethnically Chinese but not from China, e.g. Singapore, Malaysia, etc (if I got what you meant correctly).
And small-sized sampling isn't always reliable, although the website can be very subjective and tendentious. It's just a piece of advice, and not necessarily restricted to only applicants from China
I suppose, it's rather a caveat to give some good thoughts about. Given that only a handful of applicants are admitted, the adcoms might not mind rejecting very strong applicants for not appearing so to them.