Well, I tought you knew more about software than this. WHQL is not much more than a "rubber stamp", and both AMD and Nvidia have managed to ship fatally flawed drivers with WHQL certifications.
GTX 1060 runs the same driver code as GTX 1050 and GTX 1080 Ti, so when GTX 1060 keeps failing the tests and the others don't, it gives a good indication of a bad card rather than a bad driver. And it's really easy to eliminate, just use a larger sample size than 1. If there is a driver issue, then there should be a pattern. Also, when using a total of 6 different cards from the two vendors, any random piece of data would impact the conclusion, and the results could just as easily have tilted the other way.