That couldn't have anything to do with HN but all with your browser. Most likely you do have clicked through to the URI another time before when the link was up and you just forgot because it is not anything you would or could remember, higher gauge theory I mean. That happened to me with a pdf as I will save too many pdfs to read and open too many pages in tabs to fit memory.

Yeah, the only thing is I've never clicked on that link and I'm not knowledgeable enough, in any way, to understand "higher gauge theory".

It also seems I got several downvotes for my comment, trying to reach moderator dang, which I've seen other HNers do in the comments section, for example, when a title should be altered, etc.

Are you sure you hadn't opened the post from somewhere else at some point in the last couple weeks?

yeah, very sure