You are underestimating HN's reach, this happens all the time. As someone who has been on the front page of HN it's a pretty big rush in traffic!

Hacker news doesn't generate much traffic, despite what people are saying.

The host here has a limit of 160000 files served each day. That is extremely low. If the site has an icon, css, a js file and a few images it's 10 files each visit. That's will limit it to 16k visits/day. If there are more files loaded it might just handle a few thousand visits, and they have received more than that from HN now.