I wouldn't call it a hoax - it was largely a very overstated result that didn't stand up to deeper scrutiny. That isn't really harmful. The primary issue I have with this, and many related things in recent years, is people outside the community of working scientists treating "X was posted on the arXiv" as "X was published". This tends to lead to people assuming that since it appears on that site and has the layout of a regular paper that it somehow has legitimacy. We saw this over and over and over during the peak of the pandemic, even seeing regular news sources writing articles where the only source material was some random recently posted arXiv paper. I don't think I ever saw corrections published in the cases when those preprints proved to be bogus. The arXiv is extremely useful, but lots of people outside the community of working scientists don't seem to understand how to weight what people post there.

As for the "audacity of HN" - this site is a very bizarre mixture of a relatively small number of working scientists, a lot of people without much scientific background who are very interested in science, and get-rich-quick startup types who are sniffing around for the next breakthrough they can turn into money. That mix leads to weird dynamics when it comes to how scientific activities get discussed.