The oil pressure relief valve came open and blew dirty oil at the bearings. That's a common thing on an engine with a few miles, replace the oil filter mount with a new GM one, or send it out to have the valve plugged up.

The stock bottom end is bullet proof, the magic is in the pistons and tune. If the tune is off even a little, you'll chip a piston. There's also a lot of oiling mods that can be done, like porting the oil filter mount assembly, drilling the mains, modifying the pan gasket/windage tray, etc. Nobody has ever broken these engine due to horsepower, just by problems in the tune, oiling system, etc. Oiling mods are a common thing on any engine build, v8 or v6.

 

I am going to have to disagree with you on the reason why the bottom end failed. It was the center main bearing an I think Cylinder 3 that failed. Had the motor lack oil it would have been the bearing farthest away from the pump that would have starved had it been contaimination it would have been closest bearing to the pump. The motor itself was very clean. The all the bearings before the failure looked good. While I do not concider myself an expert at 4th gen I do have an accs. degree in automotive tech and was a GM master tech. One of the things I was taught was how to read an engine failure. A center main bearing failure with no other problem is most likey an engine that was pushed beyond it limits or a line bore issue. As a general rule line bore issue show up early in the engines life. This seems to be a case where the main cap bolts or the main cap itself flexed enough to allow the main bearing to spin over on itself. Course after that it blocked off the oil flow and everything forward of that was starved for oil. Not to mention it matchs exactly what I was told happened to the motor.

The other option is since these blocks are what we call green casting they can move in shape over time. If I line bored 1000 blocks today and never put them in cars and checked the line bore yearly I would guess I would see a dozen or so out of spec blocks for the first few years. It is possible that this casting had moved but not enough to cause a failure under noraml use. First time it was run hard for and extended time it failed. Also the casting process is not fool proof. Even the powder metal rods have variation in manufacturing. We do everything we can to make sure the manufacturing variation will not effect the car in its stock form in a give time range. But I pretty sure no one would reject a part cause it could cause a failure in a 600 hp version of this motor.

I don't think this is any different the the old Grand Nash days. There where guys out there that where pushing over 500HP with stock motors but for every one that made it over 500 there was 10 that did not make it much over 400hp. In many cases they where setup by the same people.