An interesting observation. Every major city of the world has Chinatown, except for Seoul. Why? Because the land is hostile enough for the Chinese to not able to take a root and prosper.
Then again, the dislike of China under the communist rule is pretty universal and nothing unique to Korea, and that Pakistan's favorable view of China is a rare exception, not the norm. China under KMT rule was actually popular in the US, and you had many American volunteer fighter pilots battling Japanese on behalf of China during the Sino-Japanese war, along with many Hollywood movies portraying China's courageous fight against Japanese imperialists.
Most of those refugees would be going back home within two years and this is not China's concern. China's concern is having a strong anti-China military presence within 600 km from Beijing, like a hypothetical USAF base in North Korea where 100 F-22 and F-35 stealth fighters along with dozens of spy planes are fielded.