I definitely saw a chat history that wasn't one I started. It was a single question and response in Japanese (which I don't know). The title in the sidebar seemed to match the conversation.

Edit: I'm getting upvoted, so I want to clarify that I don't have proof, but this did happen, only for a single chat. I dumped all the text into Google Translate (don't judge me - you'd do the same!) and it was a boring scientific question. I was amazed that it happened at all and felt pretty gross about it. Like most other people, I also saw a lot more chats in the sidebar that I couldn't open.