Moxie hasn't been affiliated with Signal for years. He stepped back years ago.

The Signal Android app is AGPL licensed. What should the lawsuit be about?

Signal used to threaten people for trademark infringement because the word "signal" was in the protocol on the wire.

I think they've relaxed this quite a bit more recently

Oracle, Nintendo and Apple have all tried this "copyrighted text / logo / poem" thing, never works out for them. For interoperability you're allowed to replicate those parts.

There is nothing legally stopping people from forking the signal app and distributing it (even configured to talk to the official signal.org servers) so long as they don’t use the Signal trademarks.

Also, as others pointed out, Moxie isn’t part of Signal any longer and hasn’t been for a while.