So I'm not the only one who went looking :) Not sure why they don't mention the specific CDN on their blog post. Possibly because they host at Rackspace but don't use Rackspace's CDN? (Which is white label Akamai last time I checked).

Apparently they don't yet have a great network of nodes in Europe though:

    ping dangrossman.github.io
    round-trip min/avg/max/stddev = 16.173/16.275/16.463/0.074 ms

(From Paris, France)

In comparison, Cloudfront is something like 2ms away.

They've been using fastly for a while now, makes sense that they're using fastly in this case as well.