Let's say you've been working in place A, you show your code to an LLM service (like the dozen or so Copilot-like services) and tell them to refactor. And for the sake of argument, let's say the LLM uses your code and questions for its next training dataset.
A few years pass, then you go to work at Place B, and ask a question that happens to be related to the problem that Place A's code solved, and they give you Place A's code as is.