I'm not spotting it. "AI" is only mentioned once.
The key and secret in the docker compose don't seem to be API keys, but keys for directus itself (which upon a careful reread of the article, I realize is not FOSS, which might be anpther reason people don't like it").
Directus does seem to have some integration with openai, but it requires at least an api key and this blog post doesn't mention any of that.
The current setup they are using doesn't seem to actually connect to openai at all.
Maybe nginx proxy manager can do this.
https://nginxproxymanager.com/