He was obviously being sarcastic about the fluffy clouds and unicorns. If you didn't catch that, then I think you're the one who is in need of medical assistance.
Also maybe your girlfriend hid the fact she smoked because she knew how you would react. Not too many people buy cartons at a time unless they are pretty serious smokers. If you think burning her cigarettes is going to keep her from touching another one, then you're just incredibly gullible. It would be pretty damn funny if she started smoking more just to piss you off. I'm not saying smoking is a good thing, but trashing her things sure as hell isn't going to help her quit.