Why do Chinese/southeast Asians/Pacific Islanders think their related to Koreans/Japanese?

Online, there are always Chinese, southeast Asians (Vietnamese, Thai, Laotian, Cambodian, Burmese, Singaporean, Malaysian, Indonesian, Filipino, et cetera), Pacific Islanders (Hawaiian, Samoan, et cetera) always claiming that their related to Koreans and/or Japanese. ? Southeast Asians and Pacific Islanders who are the descendants originated from Taiwan, island off the coast of southern China and Madagascar, island off of southern Africa, not Korea or Japan. And, the Austronesians were the inhabitants of the southern portion of Taiwan which was once linked towards mainland China, which would mean that the Austronesians are also related to the Han Chinese, also including the overseas Chinese who intermarried with Austronesians. Koreans and Japanese originated from Siberia, not from China. The physical appearances even have complete differences (eyes, nose, facial structure, bone structure, body structure). Even the cultures, cuisine, et cetera are completely different. I don't get it, it seems like people, nowadays, are ashamed of their cultures, so they try to either copy or pretend to think that their a different ethnicity. I bet the only reason why Chinese/southeast Asians/Pacific Islanders say their related to the Koreans/Japanese is because of the interest of the Japanese culture. Anyways, my main point is, just because your in the same continent, it doesn't mean the people there are all related as having the same DNA, ancestry, or origin. But, originally human evolved from Africa which was once apes. So, don't lie about your ethnicity. And, if you travel to Korea/Japan, every person there will know that your Chinese/southeast Asians/Pacific Islanders, or any other type of ethnicity. Trust me, people have different physical appearances. For example, thinking Chinese/southeast Asians/Pacific Islanders are related to Koreans/Japanese is exactly similar to thinking Latin Europeans (Spanish, Italian, Portugese, French, Greek) are related to Anglo-Saxons (The United Kingdom-Ireland, England, Wales, Scotland, Germany, Scandinavia). What's funny is that Filipino think their related to Hispanics. ? LOL. Are you kidding me? Hispanics are Native American and Latin European. They have completely different physical appearances. They only think that since the skin complexion. Who cares about skin. Hispanics are as dark as Indians, Italians, and Filipinos look so different, more like Han Chinese. I'm Japanese.