They debugged the system, not the driver. The way they did that was to identify and confirm it was the driver that caused the problem and in what circumstances

They debugged the system, not the driver. The way they did that was to identify and confirm it was the driver that caused the problem and in what circumstances, so they could report it to the people responsible for actually dealing with that. That's still a form of debugging. It's all a matter of perspective. If you had a hardware device that you were interacting directly with in an applicaiton, and you found that if you utilized in in a specific way it crashed, so you changed how the application used it so it wouldn't crash, that would be debugging the application, even if not really debugging the hardware.