I am going to guess they are getting a massive surge of traffic about now and yet the site still renders in a fraction of the time it takes most "modern" web apps or even just static content sites - this is how it should be.
Honestly, I'm not even sure what modern website are doing when they generate pages. I've had highly dynamic PHP/MySQL websites running on crap hardware, and it was trivial to attain .03 second page generation time. Didn't even need fancy caching, just some common-sense SQL optimizations.
Before going static as well I made a WP theme with Twig, removing most from there. It was fast, way faster, than the usual WP themes. Obviously nowhere close to a static HTML.