I'm curious if there is a difference between the three.
It's a UK study. The question would have been "What is your smoking history?". In the most basic case, there would be three options: "Never smoked", "Historically, but quit", "Active smoker". More advanced surveys would have examined the volume of smoking and how long ago you quit.
Marijuana is illegal in the UK, and the NHS does not typically ask questions about current drug use. Occasionally they will ask for drug use history, but the question "Do you currently smoke marijuana?" will simply not be in the vocabulary of the average doctor.
There aren't really any appropriate stratifications for UK tobacco smokers. Almost everyone who smokes uses either packaged cigarettes or self rolled. This division is strongly correlated with income. The self-rolled crowd always use filters.