It's built using Meteor, and the page is constructed on the client. You can determine this by right-clicking the page, and selecting "View Source" in most browsers.
I know how to view-source, thankyouverymuch. All I saw in my network panel is calls to analytics scripts, it appears I was mistaken. (Unlike a simple view-source, the inspector shows the rendered DOM)
Ah perhaps you mean static content then. I agree it is an odd choice for hosting static content (I'd go the static site generator route myself), but in the case of Meteor's website, I don't blame them for eating their own dog food. It helps to validate (and even test) the framework on a highly-trafficked site.