I am SO glad jofzar posted this - I remember this website but couldn't recall the company name. Here's a good video on how the site is so fast, from a frontend perspective:

https://youtu.be/-Ln-8QM8KhQ

I was intrigued that they request pages in the background on mouse-over, then swap on click. I decided to do likewise on my blog, since my pages are about a dozen kb of HTML, and I aggressively cache things.

Quick look: GSLB (via Akamai) for low latency, tricks like using CSS sprite to serve a single image in place of 20 or so for fewer round-trips, heavy use of caching, possibly some service worker magic but I didn't dig that far. :)

Basically, looks like someone deliberately did many right things without being lazy or cheap to create a performant web site.