> Is the code bad? It sounds like they had no idea he was using AI. That seems to imply there was nothing wrong with the code as-is. Why not judge it on it's merits?

Anyone that has used AI at all knows this isn't how it works. AI is extremely good at producing plausible-but-wrong outputs. It's literally optimised for plausibility, which happens to coincide with correctness a lot of the time. When it doesn't you get code that seems good and is therefore very difficult to judge on its merits.

With human written code it's a lot easier to tell if it's good or not.

There are exceptions to this - usually if you have some kind of oracle like that security work that used AddressSanitizer to verify security bugs, or if you're cloning a project you can easily compare the behaviour to the original project. Most of the time you don't have that luxury though.