Seems more like an variation of what psych and behavioral economics calls the "what the hell" effect than "power of suggestion". "What the hell" effect says once your willpower fails and you give into temptation to begin doing negative behaviors, you are much more likely to go all in (think eating a single donut on a diet then polishing off the box). By making the cancer threat real post purchase and reminding of the ultimate consequence every time you light up, they may be pushing people to throw their hands up and just keep smoking.

Of course, like this article, this is just a untested theory I pulled out of my ass.