There's not much we can tell you without a closer look (or a close up picture) - the axle is what is known as "semi floating" and is retained by the bearing, which, in turn is retained by a retainer, held in place by four studs/nuts
There are a couple of different possibilities as to what may have failed initially, the bearing is one, another is the studs/nuts may simply have come loose, and there is also the possibility that other parts may have been knocked loose or damaged when the wheel pulled out - brake shoes, springs, oil seals, etc.