That debris is way too big to be from a failing roller bearing. And, assuming it is not a limited slip differential, the only place thin, malleable stuff can come from are the thrust bearings behind the spider and side gears. When it does it's differential work of letting one axle over speed the other, those gears rotate and there is a cup shaped bearing, bushing material between them and the carrier. Shims for positioning the pinion and carrier for proper meshing of the hypoid gears don't rub or slide on anything.
