Nowhere in the HN guidelines[1] is it required (or even recommended) for a submission to be new or even recent - there are popular submissions going back to the 1900's and others that have hit the front page a dozen times because they're timeless or little-known.
The fact that the submission has 73 upvotes (as of this comment) and that I found it novel and interesting suggests that it's rather on-topic, and interesting and provides value to others, and it's certainly "Anything that good hackers would find interesting. [...] anything that gratifies one's intellectual curiosity."
Meanwhile, I don't find much value in your questioning why a popular post was submitted in the first place.
The fact that the submission has 73 upvotes (as of this comment) and that I found it novel and interesting suggests that it's rather on-topic, and interesting and provides value to others, and it's certainly "Anything that good hackers would find interesting. [...] anything that gratifies one's intellectual curiosity."
Meanwhile, I don't find much value in your questioning why a popular post was submitted in the first place.
[1] https://news.ycombinator.com/newsguidelines.html