the seal is like a large flat washer with a rubber gasket and spring in the middle.it is the last thing you tap into the hub after the bearings.
this is the inner bearing, outer bearing, races & seal. the part you have froze on your axel is the inside of the bearing assy. the bearings should have been "captured" but yours had came apart and left part of the assy on the axle. when you reassemble, you have to preload the bearings with grease(unless you have a posi-lube axle).