I've been looking at it some more and can't see where that metal could have come from.
Certainly not from the races, they are way too hard and brittle.
Not from the housing because they are typically cast iron and turn to powder when exposed to excessive friction.
It's possible it had a stamped steel cage instead of bronze but I've never seen one wear like that at all. Not even close.
The shaft seals are usually soft aluminium or bronze, no go there.
The only thing I can think of (and it's a long shot) is often these bearings are often mounted on a tapered sleeve that fits over the shaft. The ID of the inner race has a matching taper and when an SKF nut on the sleeve is tightened, the bearing is pushed up the sleeve onto the taper. They call that a taper lock for some reason, go figure
Anywho, if it failed catastrophically that metal could have come from the nut or the locking washer behind the nut. Still a long shot, it'd have to an ugly crash.
I'm still kinda leaning towards that metal shaving from a lathe theory.
DISCLAIMER: iffn this is some unusual type of bearing application and isn't a pillow-block or flanged bearing, all bets are off