MRIs work because strong enough magnetic fields will interact with any material, not just ferrous metals. This can be impacted by the structure said materials form (stents are a weave like a finger trap and therefore more prone to interaction with magnetic fields than say a solid cylinder) but I’d be inclined to say your friend was lucky. Ball bearings like in the OP are nearly always steel outside of specific high end applications and therefore would behave like they were coming out of a shotgun shell.
MRIs work because strong enough magnetic fields will interact with any material, not just ferrous metals. This can be impacted by the structure said materials form (stents are a weave like a finger trap and therefore more prone to interaction with magnetic fields than say a solid cylinder) but I’d be inclined to say your friend was lucky. Ball bearings like in the OP are nearly always steel outside of specific high end applications and therefore would behave like they were coming out of a shotgun shell.