25467 sounds like a port for a server. I haven't played yet but I read most of the comments and I studied a lot with networking and game development. If there are 12 out of 15 servers that means there are a total of 15 server slots and only 12 are being used. If only 6 are visable that means those 6 are open and the others would be "hidden" private or they are open servers but you need the port and the IP address and then enter into the console witch is probably that <o> . its possible that the chat feature is also a console like in many older games. When I get around to playing it I'll test all this out.
25467 is a valid port number.
You're sort of wrong about the slots thing. There's 15 total servers listed, 12 of them are online, and 9 of them are Capture the Flag, with the rest likely being Free for All (way more common for online shooters originally) or Team Deathmatch (much more common for more modern shooters), and are simply being filtered out. The weird part of this server list is normally, especially the way the servers are named, they wouldn't be preloaded by the game in question, which is the only way you'd see an offline server in the first place. Usually, the 12/15 means that you're viewing the 12 servers that are filtered out based on your settings, which in this instance we are forced into Capture the Flag.
This is likely the case here as well since there are only 9 servers listed, with 6 of them online. Another oddity with the server list is that one of the servers is LAN, which most games from the early 90s you had to search for using a specific filter, and wouldn't be preloaded into a server list like this, even for games that had that kind of set up (I can't think of one that used a pre-programmed list, or even showed offline servers LAN or otherwise for that matter, and I've played every multiplayer Quake, Doom, and even a few shooters that weren't that well known). Most games that did use a pre-programmed server list didn't show you the server list, and weren't shooters.
ut 2004 has preloaded servers. As do other similar fps games. Including some older battlefield or cod games on pc. The game doesn't have any other menus so we couldn't even say if it goes beyond CTF. There are some games that specific to game modes like that especially if it's close to the original doom or wolfenstein. But this game seems more like a ps1 game which would have CTF DM(ffa) and TDM. But nothing implies beyond ctf. A server typically would have multiple game modes that the host could alter. It would seem its a CTF game which throws everything under the bus. Its impossible to say what's going on I mean we could be completely far off.