Yeah, thats a medical fact. Statistically, asians have smaller ones, blacks larger ones, whites somewhere in the middle. This correlates with average birth weights for asians, whites, and blacks, and average penile sizes for asians, whites, and blacks.
I posted a peer reviewed study on this earlier in the thread.
Does Size Really Matter? | LIVESTRONG.COM
By ethnicity (age 15 and over only):
Race Size
Black 6.89" (175mm)
Asian 5.33" (135mm)
Caucasian 6.22" (158mm)
Hispanic 6.15" (156mm)
Native American 5.66" (144mm)
This correlates with vagina sizes between different races.
Baseline dimensions of the human vagina -- Barnhart et al. 21 (6): 1618 -- Human Reproduction
Evolution, in this case specifically adaption, always explains everything.