I'm not a smoker. I hate smoking. (I'm horribly allergic to cigarette smoke, and my beloved grandma died of smoking-related lung cancer.) I am all for anti-smoking programs at school, and I certainly
don't think they're rude. (Unless they're actually telling kids to confront strangers!)
That said, if DS said this to someone in a store, I'd apologize to the person and talk to him about how we do not say those things to people we don't know. (Or even most of the people we do know!)
Sometimes kids take school programs too seriously. I remember lecturing my mom about having a glass of wine after dinner when I was elementary-school aged.
(We'd just gone through a big unit on this at school, mostly about DWI and underage drinking, but I took it to extremes. Kids do.)