these things happen from time to time, my guess is there was a flaw in that particular one. the mathmatics on the design would be to spread the weight over both axles, cars were never designed to run on 3 wheels. if one comes off your pretty much out of the race anyway.
it won't be a major issue or it would be happening all the time.
and no if he'd had nuts like mine the wheel still would have come off as it wasn't his nuts that failed