Is it possible for a foreign object to be embedded in a piece of pork?
Even if a pig ate something like that a piece of jewellery wouldn't end up in the muscle (meat). It would pass through and out the other end; if it didn't have time to do that it would still be in the digestive system, which is removed before the meat is cut into portions (if you'd said dog food it might be another matter). 

I suspect that it entered the dish sandwiched between two strips,or pinned into a side of a piece that you didn't see. If you cut across the strips to dice it, it could still get in. I know from experience with diced game that you can deliberately feel for shot and miss bits. That of course would be embedded, but you weren't looking for metal in your meat. 

On the other hand, what liquids did you add? Passata/creamed/chopped tomatoes from a can could introduce something without you noticing it. 

In either of these cases it was probably removed at the start of a shift in a food factory and transferred via clothing, as it had the back on it. In some liquid foods it could have come from the farm like that but most pass through a sieve at some point. 

I assume you've checked that no one who spends time in your kitchen has lost an earring? Is hard to see how it could get into the dish that way, but not completely impossible.