However that is the cynical take we are compelled to choose because of what we know and think of smoking.

Taking only the study itself into consideration, one could easily argue that the participants "knocked it before they tried it", i.e. by taking up smoking they realized how nice it actually is.

I am not trying to revive 60's tobacco propaganda, but I would say for a lot of personality/opinion/habit/preference changes in general this explanation is very likely (and far less sinister)