The article claims that the Japanese had the MacArthur Line drawn to include Socotra Rock on the Japanese side, but I think it is possible that the Koreans simply assumed that from maps showing the MacArthur Line.
Notice in the article below that Korea thought Parangseo was a "cluster of islands" (한 무리의 섬), suggesting that it did not know it was really an underwater reef. In spite of giving the distances to the "islands" and their coordinates, Koreans could not find them and withdrew their demand that they be included in the 1952 Treaty of Peace with Japan. It was not until 1973 that a Korean man from Jeju Province named Han Gwang-seop (韓光燮) found the underwater reef. (See HERE and HERE.
Again Showing its Desire for Invasion, Japan Has Reported to the MacArthur Command that the Yellow Sea Islet of Parangseo (坡浪嶼) Is Japanese Territory
Unable to rid itself of its invasion mentality, the Japanese pirates are not only scheming to encroach on our East Sea island of Dokdo, as reported several times previously, they are once again infuriating us by now extending their ambitous scheming to the waters of the southern Yellow Sea. The problematic island is Parangseo (坡浪嶼), a cluster of islands located in the Yellow Sea at 32º 30' N and 125º E.
The island is located 150 kilometers (kms) from Jejudo (濟州島), 290 kms from Mokpo, 450 kms from Nagasaki (長崎), and 320 kms from Shanghai (上海). Just looking at it geographically, the island is without question in our territory.
Recently, the Japanese government petitioned the MacArthur Command to divide up the region of the Yellow Sea in a way favorable to them. The islands of Parang were placed within the so-called MacArthur Line, meaning they are part of their territory. However, besides being the only spawning area in the South Sea, it is also a large fishing grounds.
日本の侵略的野欲 今度は黄海 坡浪嶼に自己の領土とマッカーサー司令に報告