Most of the time copilot is giving you one-line completions that are heavily adapted to the surrounding code. It’s not “writing a book by quoting choice paragraphs from other books”. It’s fancy autocomplete.
You can direct copilot to give you anything you ask it for. If you ask it for an entire function, and you don’t give it any context, then you are more likely to get a snippet from inside its memory. But even when this happens you are unlikely to keep the entire snippet unmodified because the chance that it is what you were looking for is low.