It's just a static site. Only the CMS is "dynamic" (though it itself is just a 10 line HTML page with a bunch of client side JS that talks to firebase).

Saves to that CMS, which is hosted statically, then send a build notification to our node based build servers, which then regenerate new static html files (from template you deployed to us) and send them to the proper place. Indexing and SEO are then just as they are for any other static site.

In local development, this is done through simple watch commands in Grunt, similar to what you'd see in something like Jekyll.