You missed one crucial key points on that post:
[...]
For me, the best indicator if a post is AI-generated is if it is written in flawless English. Even the best posters who are native English speakers don't necessarily write every post using the precision in punctuation, spelling & grammar executed by ChatGPT. If a user's native language isn't English (as can be evidenced by their posting history), and they suddenly start posting in flawless English, it means one of two things:
[...]
One indicator said by nutildah is if the improvement happened in one night from a messy English to a flawless ones. I didn't look at your post history, but if I may draw a conclusion from your post above, your main language is not English and you're gradually improving your skills; vocabularies, grammars, phrases, slangs, etc. On that case, I don't see why you should feel shock or saddened with the thread, given it barely matched your criteria, nor that I find any part on that thread that encourage people, implicitly or explicitly, to deliberately "retrogress" their english writing on BTT just to avoid being detected as AI.
The forum always encourages improvement. There are literally threads filled with suggestion for non-english speakers to use a translator and then to double check the grammar with grammarly or other similar software to let them post something that's close to a perfect english.