I may be able to offer some insight here, since I'm an American-born Korean (and damned proud of it).
Koreans living in Korea don't eat nearly as much animal protein as Westerners do, nor do they have nearly as much dairy intake. They're not going to be quite as big or tall on the average. There's a good reason why those husky fellows in Nebraska who were raised on lots of corn-fed beef, end up with more muscle tissue...
Also, if you compare Koreans who live in America to those who have lived their lives in Korea, it's not surprising that those of us who have dined on the Western diet (more meat and dairy) are going to have more muscle tissue, and will be a bit taller. My cousins in Korea have a similar type of frame as I do, yet they're 3-4" shorter than I am, and don't have the same level of muscle tissue, even though some of them have done weight lifting in an effort to gain muscle tissue. Keep in mind that their folks were all of similar height / weight as my folks were, so I can probably say with some certainty that we are comparing apples to apples.
In addition to this, Koreans have lower bone densities and slighter frames. We're not built in the same way as y'all (referring to the generic Westerner) are.
While it's true that there will be an occasional standout Korean with excellent bone density and a large body frame, it's not the norm, and such individuals are going to be awfully scarce, even those who were born in a Western culture, and has had plenty of animal protein.
Think of it this way... How many folks of "pure" Korean blood are playing American football at the college level?
Anyways, I hope that this can offer some insight. Again, this is simply my own observations, and if there are valid statistics that refute my conclusions, then I will be most happy to admit being wrong.
Now you've gone and done it... I'm going to have to grab some Porterhouse steaks for dinner tonight, to be grilled to medium rare perfection, coated with my seasoning mixture (raw horseradish, crushed garlic, cracked peppercorns, seasoned salt, and olive oil).