Yes, when I was a boy, my teacher told me the same thing. The Korean troops in the Imperial Japanese army were the worst. I wonder why? Taiwan and Korea were both colonies of Japan, why did the Taiwanese behave better than the Koreans?
Perhaps, the Taiwanese were better treated than the Koreans. Taiwanese people speak Hokkien (as I do). This has some similarities to Japanese. I was surprised to learn this. Perhaps, the Japanese viewed Taiwan as a continuation of the Ryuku Archipelago. Thus they felt some affinity to Taiwan and so treated the people better than they treated the Koreans and Chinese.
The Ryukus, like Taiwan, at one time acknlowledged Chinese suzerainty. At one stage, the Ryuku Kingdom acknowledged both China and Japan as their overlord. They played both sides to keep their independence. But later, Japan got the upper hand and gradually took over. They slowly "Nipponised" the population.
Taiwan was half way to becoming Japanese, just like the Ryukuns had. As their culture seeped into Taiwan, the Taiwanese became more trusted and so rule became less harsh. That's probably why the Taiwanese, alone of all of Japan's colonies, has a better view of Japanese colonialisation.
Given, this history, Japan understandably became alarmed at China's "wolf warrior" diplomacy. China is on an imperialitic march. Will they one day claim the Ryuku as belonging to China based on the Ryuku kingdom being a vassal of China, long, long ago? After all, China claims Tibet based on something like that as well.
It may also explain why CCP propagandist claim the pro-Independence movement is led by people who were of Japanese descent or . Take Independence activist, Koo Kwang-Ming for example.
His father became wealthy under the Japanese colonial government. After the massacre by Chiang's troops in the notorious 228 incident, Koo fled to Japan where he advocated for Taiwanese independence. His son is a prominent economist in Japan. I don't know if he has any Japanese blood in him, but he is definitely influenced by Japanese culture. This is not surprising. Our LKY was educated in Cambridge and so he was influenced by British culture.
After democracy came to Taiwan, Koo Kwang Ming returned to Taiwan. He joined the Democratic Progressive Party. In 2008, Koo made a bid to lead the party. But he lost to Tsai Ing-Wen, finishing second, after he made a silly remark that an unmarried woman should not lead the party. As you know, Tsai is currently the President of Taiwan.
The Koreans were badly treated by the Japanese. Perhaps because they still had recent memories of an independent Korean Kingdom and so resented the Japanese occupation. So resistance bred harsh rule from the Japanese which bred hatred and resentment.One would think that Koreans, themselves allegedly at the time an oppressed people living for decades under Japanese occupation would have developed an almost instinctive sympathy for other oppressed peoples living at the time under Japanese rule and abstained from committing gratituous atrocities: but in practice the opposite was true. When allowed a certain amount of latitude by their Japanese officers they exceeded the Japanese in atrocities agasinst defenceless pwoplw. I have talked to Pilipinos who had lived under Japanese occupation; Australian POW's in Japanese hands etc and they all say the same: the lowest of the very low in Japanese army uniform were the Koreans.
The Korean nation has suffered greatly from 40 years of Japanese occupation and abuse; the catastrophe of the Korean War followed by the past 7 decades of division into two mutually antagannistic states. If what I have described above represents the sum of Korean peasant morality as it was in the first half of the 20th century then I can only conclude that the Korean nation deserved it all as a form of divine retribution for being such malicious fuckwits.