It wouldn't surprise me at all if ChatGPT was trained on data originating from Stack Overflow. Not familiar with deep learning algorithms but I can't imagine that it would be a good idea to have an unintended training data loop.
I agree OpenAI have something going on here, I'd assumed it was that they wanted to know the strategies we came up with for bypassing their filters, and to get into a cat and mouse game with us so that they could improve them to the point of being productized. Also, marketing, both sales, recruitment, and mindshare.
ETA: I think I underestimated before the extent to which the output is often just your own words reflected back to you, in which case, it may well be adding more signal then noise.
https://news.ycombinator.com/item?id=33863413
Still, some prompts return a walk of text from a single sentence, and I have to imagine those are worse then useless for training.