サーバーへの接続の切断中にクライアント上で呼び出されますが、切断が完了するとサーバー上でも呼び出されます。
When called on the client the connection was lost or you disconnected from the server. The NetworkDisconnection enum will indicate if the connection was cleanly disconnected or if the connection was lost. When called on the server the connection has successfully disconnected (after a call to Network.Disconnect).