You're right.
China history bases so much on legend and myth, nowadays Chinese historys reader seem to have a lot of misleading since they believe that those have been recorded in ancient time are 100% true.
I read somewhere in Mandarin that Japanese people's ancestor are eventually Chinese: that's so called "ancestor" was a Qin dynasty's official who was asked by Qin Shuihuang to sail to Japan to look for sorta "Pills of immortality". Ya, it's as interesting as a Hollywood movie.
The same thing for Korea and Vietnam