He's speaking about his objective to make ever stronger LLMs: so for this his secondary objective is to measure their real performance.
The human preference is not that good of a proxy measurement: for instance, it can be gamed by making the model more assertive, causing the human error-spotting ability to decrease a lot [0].
So what he's really saying is that non-rigorous human vibe checks (like those LMSys Chatbot Arena is built on, although I love it) won't cut it anymore to evaluate models, because now models are past that point. Just like you can't evaluate how smart a smart person really is in a 2min casual conversation.