Interesting. - Would scare the hell out of me, at first sight.
The first thought would be, how the engine ran lately...
I think this piece could be some shop debris that landed in the oil pan when it was open last time, as you say.
The way the piece broke off, there should be other pieces along with it.
Very unlikely to have a piece that size and with those edges break off somewhere, but no other pieces with it.
If the engine ran good without any change before this discovery, I wouldn't worry too much about it.
