How does this happen to a rod bearing?

I had to pull my crank to replace a rear main and found this rod bearing. The journal was in amazingly good shape. I just replaced this bearing and let the others eat. What in the heck would cause the weird wear like this?

Almost like it got water or something in there and froze and "popped" little pieces of bearing material out.

Weird.

PS. now that I look at the pic online it doesn't quite look right. The bearing is kind of pitted.

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Author: valiantone