From what I understand, lots of servers run their own custom modded games, typically based on Minetest Game. Even just for providing an enjoyable multiplayer experience, you want mods that help with e.g. protecting areas from trolls, which aren't necessary in a singleplayer experience.

If you run /mods in the chat of the server, it should list the mods it uses. You can try to compare that with the output of /mods in a locally running Minetest Game world.

But it's also possible that they use custom-edited versions of mods or entirely newly-written mods, which aren't separately published. I'm pretty sure Luanti just downloads the mod files from the server onto your PC, so you can probably find them somewhere and use them in a local game.

I can't find anything about it either. You might want to try to get in touch with the server operator to ask about it