The blog post mentions rising standards of quality enabled by AI-assisted code review, and that reverted code predates the era of AI. Even very competently managed codebases are not above mistakes, especially when held to as high of a standard as this.

Well I have a document for you to read on this very question!

Take any codebase you built in the pre-AI era and run it through AI review. I guarantee, no matter how smart you are or how diligently you write tests, you will be absolutely gobsmacked by the findings. Turns out we haven't been writing perfect software all this time and we have some catching up to do.