Basically that's true, if the client does follow the Gnutella protocoll and uses only one port (e.g. TCP port 6346).
But I don't think that question is easy to answer, as long as we do not know what the purpose of those other ports is. I think the Unregistered misunderstood at least the meaning of the force_IP setting (which is no port number, but an IP-address used for sharing behind NAT routers/firewalls), actually Mactella describes various ports in the documentation. I asked the developers by email/PM and in their forum (Limewire, Mactella), got no answer.