Users submit random web pages that pique their interest. Those who are merely scrolling through the “New” page find these submissions intriguing as well, leading them to upvote. These submissions gradually ascend to the top of Hacker News in place of other submissions that are typically more relevant and submitted during weekdays.
Similar, but not quite the same as https://xkcd.com/1053/
In short: somebody thought it was interesting enough to submit, and enough other people voted for it that it got to your attention.
That's it.
If it ends up with 2000 points and sits on the new page for 3 days, I'll be quite surprised, but strange subjects do that.