No one said it was "all about collectivism"

What is being said is that collectivism is a common theme within Chinese philosophy, which it is.

A good example of this is religion within China.

Buddhism and Daoism- both about helping others, and being communal, the collective outweighs the singular.

Abrahamic religions - about individualism, helping others is minimal, the singular outweighs the collective.

Also; Yang Zhu was regarded as a hedonist, not a philosopher, and was an outlier.

Much like we have people who believe in communism in the west, there's individuals in China who follow capitalist ideals. That doesn't make capitalism the majority belief within China, and doesn't make communism the majority in the west.

That's like saying "well, there's billionaores in the west so everyone is a billionaire", that's not how it works.

You seem to believe that a few individuals within a society believing something the rest of that society doesn't, suddenly makes that society about that individuals beliefs.