Didn't people find it bundled with a bunch of other things in a single runtime? Downloaded as part of a whole runtime would suggest it wasn't downloaded directly from the source.
I think it's not baked into codex, but codex has either been instructed to download it when asked to edit word docs/excel spreadsheets, or it picked it up during training.
i think that's a perfectly coherent and reasonable way for both these apps to work.
people don't want AI features leaking into their non-ai apps. I'm not an AI hater - I want my AI app to be able to read and write word docs, but when i decide to open up libreoffice i'm doing that because i want to write something myself, not use AI. i don't need my word processor to bundle an inferior version of what the ChatGPT can do for me.