If you pay attention this isn't a UTF-8 decoder. It might be some other encoding, or a complete misunderstanding of how UTF-8 works, or an AI hallucination. It also doesn't talk about how to handle the variable number of output bytes or the possibility of a continuation sequence split between input chunks.

I paid attention and I don't see where Daniel claimed that this a complete UTF-8 decoder. He's illustrating a programming technique using a simplified use case, not solving the worlds problems. And I don't think Daniel Lemire lacks an understanding of the concept or needs an AI to code it.