Bearings are pressed into the block, and oil is forced under pressure between them and the crank's journals. When spinning, the crank rides on a thin layer of oil. Unusual forces, such as detonation, can cause additional loading on the crank. This loading can squeeze the oil out of the clearance, and this increases the chance of metal-to-metal contact. In other words, you could have a bearing failure, which was actually caused by detonation.