Well, it looks like they may have a default open policy (ie everything is allowed) and may have decided to only close the "most dangerous" ports on their firewall.

The only reason nmap is reporting napster on that port is because it's defined as such in nmap-services (on my fbsd that's located in /usr/local/share/nmap). If you run napster on port 80, nmap will happely report an open 80/tcp http port eventhough napster is actually running on that port.

Without the banner grabbing mentioned above you won't know for certain what the actual protocol is that's running on that port. Since port 6699 is filtered you cannot do a banner grab and therefor cannot be certain what's running, for all we know this port is closed (on the machine itself) and blocked by a firewall.