Signaling server connection, room connection, and peer-host connection are all different things. You're looking for the multiplayer - room - disconnect action, which will disconnect the host from the peer (and leave the signaling room) not multiplayer - signaling - leave room.
You can leave the signaling room (or even disconnect from signaling entirely) after making a connection with the host, and still be connected to the host. When you refresh/close your browser window you are finally closing that peer-host connection.
Regarding the kick feature you need to use peerid, not the username.