Wrong framing. The parent didn't set it up as a means to filter. In your situation you have a list of applicants that you are filtering. In the parent's scenario they do not yet have applicants, they simply ask their network if there's any suggested candidates which then forms the list that they will filter from.

It's as discriminatory as posting on Linkedin but not on Indeed. The discrimination would come from the counterfactual question of: supposing they posted the job listing to a larger network _and_ supposing a clearly more qualified applicant applied, would that better applicant be turned down due to nepotism. That's the difference. No one is getting upset at family businesses despite almost certainly failing the counterfactual.