You'll probably never find where it came from. I doubt seriously that it came from inside but somehow was left behind when dropped. It certainly doesn't look like it was a structural engine part that broke loose - it's uniformly too thin. I wouldn't worry about it. Check your magnet again on next
oil change. Do it sooner if it concerns you.
To me it looks like a decorative piece that came off and somehow got into the engine. The shape reminds me of the front bumperettes. It's a chromed something or other...