The HN guidelines say "Please respond to the strongest plausible interpretation of what someone says". The way I understand it is that different people on the thread often have different ways of thinking about the topic, and we shouldn't dismiss something because it's not what "we" were talking about. In this case, it was obvious to you that the parent was talking about smoking tobacco, right? So you can either engage with it, or not, but there's no need to reject someone's comment for not adhering to what you decided is the topic.