Teardown results are in the article.
"What happened? That’s a good question, one that wasn’t answered conclusively even following a complete teardown at GM’s powertrain headquarters in Pontiac, Michigan, where the engine went after it was removed by our local Cadillac dealer. The damage was limited to the even-numbered cylinder bank, with cylinder six taking the brunt of the carnage; its cylinder walls were scored, and aluminum plucked away from the edge of the piston and sprayed on top of it as well as on the exhaust valve. The severe temperature and pressure also blew off the ground strap at the end of the spark plug, and even the cast-iron cylinder liner showed some pitting.
Bad fuel could have caused this kind of pre-ignition or knocking, but then both banks would have been affected. So small-block assistant chief engineer Mike Kociba thinks it was likely one of two things that happened: Either the fuel supply on that side of the rail was somehow depleted—a contaminant restricting the flow somewhere—or a similar blockage in the cooling system that allowed things to get too hot. But, during the teardown, they didn’t find such a blockage in either system."