Not the author, but I think the idea is to avoid overloading the meaning of 404. They argue 404 should mean the request didn't match a known route, in case the request is recognized but the record itself isn't found you should return a different 4xx code

I kind of get this and wouldn't complain about an API doing this, but I also wouldn't be surprised for `/api/v1/posts/abc-123` to return 404 because the route handler couldn't match the post ID.