A DDOS of HN is quite strange indeed. There should be some kind of ransom involved, but seeing as HN doesn't make money (I assume) from these forums, there is nothing to ransom.
HN has a big table of closures representing actions a user can take. Loading certain pages, such as the reply link on a comment creates more of them. They time out after a while, which will get you "unknown or expired link". Intentionally creating a few million of them ought to fill up the server's memory and would be a more effective way to to impair the server's functionality than simply requesting the home page a few billion times.
Which is to say the blog post about it probably wouldn't be worth reading :)