They were tight when he put them on, the car passed tech inspection.
The explanation was given to me by people who are far more mechanically inclined than me, e.g. they bring their race cars to SCCA events in covered trailers.
Apparently the threads on the wheel studs were different than the threads on the lugs. The felt tight because some portions of the threads were in contact with the lugs and sufficient to hold the wheel on when the car was stationary or moving slowly.
However, as soon as the car reached a certain speed, enough force was generated to rip the threads out of the lugs; the threads in the lugs themselves were stripped out of the lugs are were laying on the track and stuck to the guy's new Toyos.
The example given to me was of an old car whose wheels actually rusted to the hubs; you can beat the wheels with a mallet and shake the car back and forth and the wheels won't come off, but you can then drive the car slowly and they will loosen enough that they can be removed.
I suppose that a really experienced racer (like the guys that figured out what happened) might have recognized that the lugs were wrong, but weekend amateurs- like me- would probably assume that the lugs were OK as long as you could torque them to the proper setting and they felt like they were properly affixed.
Bummer for the car, it was really, really nice- pristine condition. Hopefully the tire company owns up to its mistake and does the right thing so he can get the car back on the road.
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