If you are suspecting that the metal came from the crank, it would be a good idea to pull the engine and split the case to examine the crank. Adding new pistons to a bad bottom end may be throwing your money away. It doesn't take much to get the engine out of the bulkhead and splitting the case is pretty easy. It's hard to tell from your pictures if the piston is usable, but if it were me and it had any damage, I would replace it. Or both.