Taiwanese in Post WWII Korea?

I've been thinking about the author's note for Vern Sneider's 1950 short story, "A Pail of Oysters," that was published in the Antioch Review. It notes that Sneider first met Taiwanese in Korea:

In early 1945 he served as area supervisor of Tobaru, a village of 5,000, on Okinawa, and later went to Korea where he was given charge of the education and welfare sections of Kyongi Province, which contains Seoul. It was on the last job that he first came to know well the various Chinese groups from whom he gathered the material for the present story.  “Whether they were Fukien, Hakka, or Pepohuan,” says Mr. Sneider, “their grievances against the soldiery were always the same.” Afterward, he and a group of Chinese intended to create a fishing fleet, build food processing plants on the Pescadores Islands off Formosa, and distribute their products through the East. The situation became too “chaotic,” and he came home where for the past three years he has been trying to “bring the desperate plight of Asia to light through fiction.”

My question is about what these "Chinese groups" were doing in Korea? Were they former soldiers for the Japanese empire? POWs?