They weren't talking about a smiling addiction (whatever that means) or any other random addiction. Denying that you have a cannabis addiction says nothing at all about any other addictions you may or may not have.

They were talking specifically about cannabis addiction, and suggesting that denial that you have a cannabis addiction is a sign of having a cannabis addiction. (However, this doesn't really make sense because people who are not addicted to cannabis will equally claim to not be addicted to cannabis.)