Good question, because having lived in Korea for a few years and having many Korean friends I’ve never met a Korean who believed that Confucius is Korean or that Koreans invented Chinese characters or any kind of foolish thing like that yet all the Chinese I’ve met seem to believe this about Koreans. I wonder why.
I’ve had a few Korean friends who lived in China and all of them told me that Chinese asked them this question, which puzzled them. Here’s a Korean friend I have who lived in Guangzhou for a few years for example:
And many more of my Korean friends asked me why Chinese people ask them that, and I’m not sure why.
If I had to guess, since I’ve been hearing this from Chinese friends for at least the last 10 years now, it’s likely that some Chinese back in the 2000s found a Korean nationalist posting crazy stuff online like Chinese originated from Korea etc or Confucius was originally Korean etc, then spread the rumor online that ALL Koreans must believe this, and it’s now widely believed by Chinese. Even these days, I found Chinese posting nonsense stuff here on Quora about what Koreans purportedly believe or think, who obviously haven’t asked any Korean person about it at all.
Here’s some examples I found of this. I think the equivalent would be if somebody found Kanye West posting anti-semitic stuff online and then told everyone that all Americans are anti-semitic because Kanye West posted that. It’s ridiculous..