If that's all it was, there'd be no distinction at all.
Men, broadly, have plenty of "relationships" that they invest themselves in and are extremely loyaly to.
What the study was about, and the discussion is about, is emotional support, and that quality is often not seen (or at least acknowledged) in the intense, loyal, committed, and earnestly worked on relationships that men do form, because its only one quality among a whole plethora that might define a relationship.