Unturned has an anti stream-sniping system where it changes everyone's name in game to Nelson. This is to stop people from harassing you in game or targeting you because you're streaming content. Streaming mode also makes it so people cannot join your game through your steam user page unless invited to your game instance. This may automatically turn on if the game or steam detects that you are streaming.
To turn off streamer mode, Click Configuration, then Options, and then unselect Streamer mode. Now that Streamer Mode is off, you'll be seeing everyone by their Steam Names instead of "Nelson."