The average black male is not using okcupid
OKCupid has millions of people that use it everyday. This is data collected from real people, and it's not a stretch to infer those results to real life as we see it ourselves all the time from thirsty black men.
And just because they are likely to be married to black women does not mean they desire white women more. Black men are thirsty for white women. But their thirst isn't reciprocated (says okcupid). It isn't mutually inclusive.
To be sure no one even knows if this is even true, but results from okcupid are not as meaningless as you suggest.