I believe robertwiblin et al.'s point is that ceteris paribus working for yourself that features these characteristics will make you happier than working for yourself and focusing on other things.

In the original article, they clearly identify that some things (e.g. competence) can change over the course of a career. Hence "pre-condition" is a strange way to look at the research.

It doesn't necessarily provide those things certainly. But inasmuch as it makes people fulfilled, it will mostly be because working for yourself is providing those things. :)