When the seat disintegrated and then the piston hit the valve insert material, then the oil that is used for the boundary layer lubrication can get squeezed out and then the bearings go metal on metal and the bearing material will shear/smear...
Great Explanation, oil for boundry layer got squeezed out from the extream high pressure of the piston bottoming out against the seat material sending the presure down to the crank bearings.
The bearings are the weak link in the rotating assembly to hammer out first and protect that important crank shaft when things go bad.
The Bearings did their job, protecting critical machine work around them.