I'm not sure if any name can be truly "copyrighted".
Obviously, names like Sky, Moon, Flame, or things like that are really, really overrated and popular so of course you would see them anywhere. No one is stealing anyone's name in this case.
However, it IS a bit annoying to see someone copy another name if it's really distinct or unique. Most of my characters have 'weird' names, that stick out, so I would probably notice if I saw someone running around named Yofiel or Sandalphon, both of which are names of my characters. They're unusual, so if I saw someone with them (and also having their in-game character look similar), I would know they copied.