This is one of the things I've mentioned before, I think it's just hidden a bit and hard to see, but this is basically the LLM doing style transfer, which they're really good at. There was a specification for the code (which looks like it was already trained into the LLM since it didn't have to go fetch it but it also had intimate knowledge of), there was an implementation, and it's really good at extracting out the style difference between code and spec. Anything that looks like style transfer is a good use for LLMs.

As another example, I think things like "write unit tests for this code" are usually similar sort of style transfer as well, based on how it writes the tests. It definitely has a good idea as to how to sort of ensure that all the functionality gets tested, I find it is less likely to produce "creative" ways that bugs may come out, but hey, it's a good start.

This isn't a criticism, it's intended to be a further exploration and understanding of when these tools can be better than you might intuitively think.