I don't know why anyone would paste or type secrets into codepen which is public by default... But it always seemed like it auto-saved / sent your code over to the back-end, going back ten years roughly?
It's also a foolish thing to do. Any time anyone types anything into anywhere on any webpage, that data is as good as gone, it's out there. Back in the 90's I experimented with per-character logging on all form input boxes, just because I could. That's still possible today.
