The people who were selected into the study were not necessarily "habitual coffee drinkers". The only requirement was "was a habitual coffee drinker sometime in

The people who were selected into the study were not necessarily "habitual coffee drinkers". The only requirement was "was a habitual coffee drinker sometime in the past five years". The difference between the two is subtle, but its possible there were people in the study who had already abstained for some amount of time.