Right, its a joke, in the sense that the phrase “Caliph” started its usage in a non-serious fashion that got a chuckle, but the way Zack uses it, it really doesn’t feel like a joke. It feels like the author genuinely wants Eliezer to act as the central source of authority and truth among the rationalists and thus Eliezer must not endorse the heresy of inclusive language or else it will mean their holy prophet has contradicted the holy scripture causing a paradox.