They are non capitalist organization because of how the decisions are made in the firm.
In a capitalist firm you have a owners, board of directors, and key employees aka top management make all the decisions of the firm and the workers have no say in what goes on.
Capitalist firms appropriate the surplus value of workers.
In Worker Cooperatives the worker decides on what to produce, how to produce, where to produce, and what to do with the profits. The worker is not exploited because they decide collectively where their surplus labor goes opposed to have a boss who decides where it goes.
Worker Cooperatives are a democracy as in one member one vote while regular capitalist firms are a totalitarian environment who those who have more invested financially in the firm are the people who call the shots.
Worker Cooperatives in the industrial era were started by socialist who were following of Robert Owen. Robert Owen was a pre Marxian socialist.
The Mondragon corporation in the Basque region of Spain were started by a priest named Arizmendierreta who convinced everyone that if they wait for capitalists to come into the area to create jobs they would die of old age so they went about creating worker cooperatives.
They have a distinct anti capitalist attitude when they compare them selves to other kinds of businesses.
Many of the hardcore leftists, communists, of Italy were the ones creating laws that would help worker cooperatives grow and flourish.
So if you don't agree that they socialist... one thing is for sure... they are not capitalist.
They are not privately owned but collectively owned by a private group of people.
They are fundamentally different other than they both can exist in a market system where goods and services are given to the higher bidder.