Does the author genuinely believe that no one wondered in the ten thousand years between our earliest example of tobacco use and 1820?
30 seconds on Wikipedia would have given you context of when the separation of nicotine occurred. Kind of hard to guess how tobacco plants make nicotine when you don't know what it is.
Either way somebody somewhere wondered about this before 1820.
I find nicotine to be an underperforming chemical, despite its popularity. A bit more of a cognitive kick would be nice. Know what I mean?