The assumption about the driving has nothing to do with one's ability. It has everything to do with the fact that many people dealing with mental illness cannot afford to operate a car. For instance, the majority of the people including myself attending support group are on disability. Owning and operating a car is simply a luxury that most of us don't have. To hear of people with mental illness whose lives have not been affected by such definitely would be a surprise. This is no indication of slighting of your capabilities but yes, it might still be insulting.