If so, why???

I have a wing, who's Asian. He says he's only into Asian girls, and won't approach women of any other race when we go out. Unfortunately, from what I've seen and heard, Asian women usually stick to their own social circles and they usually hang out with their friends rather than go to bars/nightclubs for fun...at least this is what I've observed here in the East Coast. So, whenever we go out, he doesn't approach because there aren't many Asian women around, and I feel like I'm doing all the work while he just watches and gives me theoretical advice based on what he saw and what he's read. But, I digress...

I'm just curious, do most Asian guys just stick to their own race? And if so, is there an underlying reason for this?

So where do mixed asians come from?

Sorry, the facetious comes out every once in awhile. True, people of the same race tend to attract each other, but that's not some kind of rule. There are tons of factors involved...like language barriers and family ties. I'm not sure how it works back east, but here in the midwest, asian girls go out just like all girls...and asian girls go home with dudes of every color. I'm part asian and I prefer blondes. My roommate is half Korean and he'll fuck anything with a vagina and under 300lbs (sometimes he makes an exception, lol)

To me, it sounds more like...
"I only like asians" --translation-- "I'm too scared to approach"

Well, I'm not asian and I only go for asian girls... (Kidding, but I do have a preference for them.)
Even if that's true, their friends may NOT be asian and therefore go out to bars nightclubs for fun. Also, I've definitely seen roving packs of asian girls running around here in Buffalo once in a while. Also occasionally see them alone or with non-asian friends. My sense is that girls from asia stick to their own, but American women of Asian descent aren't like that. It's probably more to do with shared language/culture than anything else...
I'd say in your friends' case it's probably approach anxiety. Maybe test it and bar hop until you find some Asians, then see if he'll approach.
You mean, aside from asian women being really, really hot?