Will dig deeper on this but at first glance this is more involved than my concept. Not a dig at the author at all, I’m just thinking even more simple.
Discussion
it's basically replicating the IRC protocol with nostr, in case that isn't clear
messages are cached in a thing like a chanserv, and access to a given chatroom is controlled by a list created by the channel owner, which controls which npubs can access the data in the chanserv
i haven't done much more thinking about it since i wrote that