Did you mean to reply somewhere else? This doesn't seem to relate to what they said.

I think it's a joke on the claim that Twitter would become an 'everything app' when it became X. The software X11, being a windowing system, actually is a system for running 'every app', in a way.

X11 is a protocol, not a window manager.

Good point; I've edited my post so that it's more accurate.

Yes that was the joke :)

Maybe they were joking comparing the logo flip with the way X flips the regular notion of client and server (you run the X server on your machine, and you connect the remote app as a client).

Yeah woops. There was a comment that said the X logo looks like this X’s logo, but flipped