Just because you find a small percentage of Asian dudes with big dicks doesn't mean that the general rule is untrue. If I said that Asians are shorter than the average Caucasian or African American, you can't drag out Yao Ming and say, "See, you're stereotyping Asians. Ming is really tall, so that means that all Asians are tall!" It's ridiculous.
All you have to do is visit a bath house sometime and look around. I've done that hundreds of times, and 99% of the Asians have small cocks. I've run into a grand total of TWO Asian dudes who had impressive cocks, and one of them told me that he's grandfather is African American. The other was adopted and didn't know his full heritage.