This is because the pronunciation of each Chinese character in Korean is close to the Chinese pronunciation. One of the purposes of King Sejong's organization of scholars to invent the Korean national script is to record the Chinese pronunciation of each Chinese character in the national script. Come down so that Koreans can easily pronounce it to promote civilization.
Korean names are also based on the seniority in the family tree plus a Chinese character with a beautiful meaning. Of course, the pronunciation is similar to that of Chinese names, and the meaning is also similar. Of course, in recent years, Koreans have stopped naming names strictly according to the seniority in the family tree, but most people still choose Chinese characters with beautiful meanings. This is similar to the evolution of naming methods in our country. Only a few Koreans have begun to use inherent words to name names. Therefore, there are also names such as Kim Hanon, which means Lord's grace, and it looks like a Catholic name at first glance, Li Hana, which means Li Yi, Jang Nara, which means nation, etc.
It must be pointed out that although the way North Koreans choose names is the same as South Korea, because they do not directly use Chinese characters, they cannot directly write their names based on the Chinese characters on their national certificates like Koreans do, but need to guess the meaning. Later, Chinese characters were translated according to similar pronunciation, but in many cases only the person involved knows what the name is. For example, Kim Jong-un was originally translated as Kim Jong-un, but it cannot be wrong because the pronunciations of Jong-un and Jong-un are exactly the same in Korean. How to write it can only be determined based on the official Chinese translation of North Korea.
As for saying that Korean names sound like Mandarin, I think it is inaccurate. In fact, it is more like a southeastern Chinese dialect, because the pronunciation of Chinese during the reign of King Sejong the Great moved southward.
For example, Jin Aiguo, whose Korean pronunciation is kim ae kook; another example is Li Renjiang, whose Korean pronunciation is lee in gang. Does it sound like Mandarin or Shanghainese? I think it's obviously more similar to the latter.