Those main bearings look like they were oil starved. The crank appears not to be floating on the correct film of oil. Cause: excessive main bearing clearance. The wear is clearly shown in the upper and lower part of the mains indicating the crank was "thumping" up and down. This engine was in the beginning stages of failure, in time one of those mains would seize and spin. A properly lubricated main should show no "wear", a bearing with 8K miles should look new.
WHAT are you talking about there's no pic of upper bearing. From what I'm seeing it's normal bearing also it's not tri-metal bearing. Part it did wear through just over lay to protect the bearing. Excess bearing clearance crank won't tick you get low end knock. But I mean it has to be excess to get that noise. Do you really think crank rides on firm of oil LOL. It slides across the bearing oil just helps it plus take heat out of bearing/crank to help it from overheating/galling up. I'm not seeing signs of oil starvation. I see bearings in heavy truck engines with million miles look just like that and crank is perfect.
They may have just told him something and then just replace it whole engine never telling him real reason.