It's not that anything in the verification protocol needs to be human-readable, it's that domain names themselves need to be human-readable and therefore can't just be derived from public keys. Which means you have to have some kind of system for deciding who controls which names, that doesn't just come down to who possesses a particular key. Zooko conjectured that this couldn't be done in a way that was both decentralized and cryptographically secure. He turned out to be wrong about that, although the DNS that everyone actually uses remains centralized.