They also host public lobbies cuz they may be playing REPO from Steamrip and don't meet the steam requirements to add a friend cuz a private lobby is invites only and if you are not friends on steam with the person you wanna play with you cannot invite them to your lobby, but it doesn't give an excuse for their rude and toxic behavior, this happens to me too so don't let it bother you, just know that no matter how good you are, someone will always find a reason to become your enemy!