If you simply ping a server (like JJ2 automatically does), it will not show up because the number is simply too small to consider (32 bytes/ping). When you are connecting to a server, larger amounts of packets of information is being sent for various queries (i.e. Is this an unknown tileset/level?) and after this visible information is processed, either the required downloads the query listed will begin, or the level will start and the user has joined.