Sorry.

Fatigue is a two (really three) stage process. Ignoring crack initiation, stage 1 would be the part where a crack grows slowly with virtually zero overload for a while, and is characterised by deformed and worn surfaces to the crack - where the crack has repeatedly opened and closed/moved, bringing those crack surfaces together again and a again. The second stage is the catastrophic failure part, where the remaining material is too small to hold the load anymore. Normally, the first stage takes hundreds or thousands of cycles, so that worn area will be polished and smooth and shiny. But in cases where it has only taken a few cycles before failure, it won't have ad tiem to polish or smooth and will be dull and rough.

Second; all metal components start off life as castings. Then they're forged and shaped, etc. Aluminium is prone to oxidation, and the vast majority of manufacturers of the bulk alloy either don't know or don't care that there are set rules as to how fast and how far you pour aluminium, and any other alloy that readily oxidises that readily. You throw the metal into the mould turbulently and the surface film of oxide which is dry and hard wil be wrapped up and dragged in into the casting. Long story short, all Al alloys, all stainless steels to a lesser extent, Ti alloys, Mg alloys suffer this problem. These films are cast-in cracks. Sometimes they weld up during forging, sometimes not. Especially wil Al and Mg alloys. I've never seen it in a rim before, but I've seen elsewhere Al components that have failed from a film-crack that survived forging and went on to remain in a component.

Unlikely, but possible.