Eh depends on who is advocating for you, but yeah generally it doesn't matter. I can also see a scenario where if they want to accept you they might go to the person you listed and be like, "so we are considering accepting X, they said they knew you. Are they actually a serial killer in disguise?"Maybe they do med student interviews and want to ensure that you don't get matched up with someone who knows you? Not sure. It almost certainly won't give you a boost.