I’m not an expert but in my opinion, if there’s metal in the crankcase from bearings... the metal from bearings tends to be little tiny flakes. Metal from gears is more of a dark black dust consistency. But bearing debris is made of chrome flakes. It’s a very distinctive sort of debris.
Now granted, all the above is a rough rule of thumb. There will always be the odd case which none of the above applies such as flakes coming off of bearings which is the sitting in a crankcase for years which has water in the bottom of the crankcase. That might get rusty. But, I would think most bearings shed bright flaky metal.
