You're surprised that people assume your comments are on-topic? I'm surprised by your surprise. In general, when everybody is talking about a topic and you add

You're surprised that people assume your comments are on-topic? I'm surprised by your surprise. In general, when everybody is talking about a topic and you add something to that discussion, they will try to interpret it in a light that makes it relevant. That's just how our brains process communication. If you intentionally mean to go off-topic (which you usually shouldn't, but we'll assume you have something really amazing to say), it's best to explain that you're not actually talking about the topic at hand but you thought it was interesting because X. That way people will be able to read your comment in the light in which it was intended rather than straining to find relevance. (Incidentally, I have no idea why you responded this way to my comment, which is explicitly about ways to ensure people read articles before voting on comments about the articles, and is not about you at all. Maybe you assumed it was on the topic of your comment?)