You're absolutely right. The article claims you can't define pornography by deliberately choosing a few borderline examples, and pretending that's all there is.

It's simply not a good way to discuss the online safety act. One could apply the same kind of reasoning to theft: "I took a friend's car without his consent, but I returned it, with a full tank. It would make zero sense for him to denounce me to the police. They wouldn't even think of prosecuting. People borrow things all the time."