One drink a day is seven a week. If your family describe you as regularly having more, I doubt you're having eight. More likely you're getting drunk on a regular basis.
The cohorts are fairly clearly separated into "doesn't drink," "drinks moderately," and "drinks heavily." They have to define them somehow, and "regularly drinks more than one drink a day" seems like a good way to do so.
I'm sure some people are misclassified in both groups. If you're improperly classified because once a week you have two glasses of wine rather than one, I doubt your risk is that much higher. That said, moderate and heavy drinkers saw the same rates.
