irc.rmrk.net simply forwards you to where the channel currently is (currently irc.acidchat.net). That way if it ever moves networks again (it's moved 3 times already), nobody needs to change any settings and old posts saying what to connect to will still be correct.
The title is "irc.rmrk.net back up" because it was only irc.rmrk.net that was down, acidchat itself was up.