[Double_Cast]

> why bring -isms to the study in the first place?

The article isn't bringing "-isms" or ideologies into the article. The article intended to contrast the Modern West's economic system [0] with the Feudal System. But you are interpreting the article to have contrasted Private Ownership with Public Ownership.

> the claim that it's a "myth of capitalism" makes no sense.

It makes sense under an interpretation you seem to have missed. Colloquially, "Capitalism" means different things under different contexts. Furthermore, it's possible to classify types of economies along boundaries other than Private Ownership vs Public Ownership. Analogously, there's more colors in the rainbow than just Red and Green. Attributing a property to Red doesn't necessarily attribute the opposite property to Green. Consider the possibility that your interpretation of the text was not the intended interpretation.

[0] which in reality is not a Free-Market Economy, but more accurately described as an Industrialized Mixed-Market Economy.