I once asked ChatGPT for an opinion on my blog and gave the web address. It summarized some historical posts accurately enough. It was definitely making use of the content, and not just my prompt. Flattered me with saying "the author shows a curious mind". ChatGPT is good at flattery (in fact, it seems to be trained specifically to do it, and this is part of OpenAI's marketing strategy).

For the record, yes, this is a bit narcissistic, just like googling yourself. Except you do need to google yourself every once in a while to know what certain people, like employers, are going to see when they do it. Unfortunately, I think we're going to have to start doing the same with ChatGPT and other popular models. No, I don't like that, either.