Well it's obviously not true, but it's generally said by people who do have trouble telling Asian people apart for whatever reason. I could almost understand someone having this kind of difficulty if they don't often see Asians around them, but in his case, he does have tons of Asian friends in his circle, so I really don't get it. :S
I told him when they open their mouth I would know =p
In any case that guy you're referring to was probably just kidding. I know I like to mess with some people who thinks wielding a chopstick is magic.