They say they trained it on databases they had bought access to etc. And it seems that way.
Because how does ChatGPT:
1. Do what you ask instead of continuing your instructions?
2. Use such nice and helpful language as opposed to just random average of what people say?
3. And most of all — how does it have a structure where it helpfully restates things, summarizes things, warns you against doing dangerous stuff… no way is it just continuing the most probable random Internet text!!