You are completely missing the parent's point. They say that this is one of the examples where hires are not performed 100% based on merit but that existing networks and references are an important aspect, without denying that this person did not have the merits to be hired.

Also, yes, good job histories, friends and communities are not limited to white males. But they have a strong component of inertia: if those communities, jobs and friend networks have something in common (e.g., gender) it is only normal that they attract persons with that trait and therefore the bias persists. Changing that is difficult and takes time and effort.