I think race used to be a factor a long time ago. This was because people of the same race would interbreed. Therefore, the genetic traits would generally be passed on within
a certain population, and contact between different populations was rare. In the end, the members of each population would have similar traits. That's why we have distinguishing factors such as facial features, skin color, hair color, eye color, etc. to determine our race/ethnicity.
However, now that the human race, along with the help of our world leaders, are aiming towards globalization and interaction between different countries/continents, there is more interaction between various communities. Babies are more frequently becoming multiracial. Couples are becoming more diverse. For example, I'm 100% Filipino, but I know many people at my school that could be 50/50 Filipino-Italian, or 50/50 Swedish-Mexican! Now that our genetic traits our becoming mixed, the distinguishing factors (hair color, face, eye color, or in this case penis size) aren't necessarily associated with a certain race.
There are exceptions to this, however. There are many isolated communities in Asia, Africa, and South America that still don't have any contact with the outside world. These are poorly developed villages that are not globalized, and not much foreigners visit these areas. Of course, the genetic traits within that population will still be maintained.
Therefore, what I'm trying to say is that, in this day and age, penis size is not associated with a certain race, unless that race is still isolated from global development.
I would like to thank my biology teacher for teaching me all this stuff about evolution and genetic traits; I wouldn't have been able to answer this question without you. (sigh)...I definitely need to get paid for this.