This is interesting, but, the "nothing but AI" part is clearly not true and so I'm not exactly sure what was done here.
The Twitter thread shows exactly what the AI made. It was used for the JavaScript code and the image assets.
If you don't have a Twitter account you can see the full content on Nitter https://nitter.net/javilopen/status/1719363262179938401 or in my Gist copy: https://gist.github.com/simonw/f7ed52daaa66f849858d17e0d6c1c...
Why is it not a game? I even played it a bit -- was I hallucinating?