The section of "vegetable drugs" also includes things like peppermint and watercress, as well as more obvious drugs like tobacco, coffee, sugar, chamomile, etc.
There is a point of view (in fact, a very useful one!) that "food is just one category of drug" - meaning, something consumed that has a physical and/or psychological effect. But, even that aside, most of these things have traditional medicinal use, and there is an archaic use of "drug" to mean "any ingredient used in chemistry, etc."
I've always taken that column as just "plant-related things I'd like to catalogue."