This like most federated systems is AP. Cut a federation link and you create two or more different state views.
From the screenshot on the project website, it seems "@serv.er" is part of any remote nickname, so I'm assuming the nicks are in per-server namespaces, which prevents any nick collisions.
Although it must wreak havoc on many IRC clients, since the @ sign has a very specific meaning in the IRC protocol. :)
That’s an old screenshot, which should be redone. We switched to :, so, it is now nick:example.com.