BTW this happens all around the world. There are some staple dishes found at every Chinese restaurant in Korea, which are only tangentially related to Chinese food sold anywhere else.
Korean-Chinese cuisine is its own thing. Many of its staples like tangsuyuk and jjajangmian are based on Dongbei cuisine (Northeast China, next to Korea) and Shandong cuisine (across the Yellow Sea from Korea), which are both fairly uncommon outside China.
