I will have to relook at this - the comment is from a year ago when they weren't using React.
On a cursory look, it still seems to use a Node.JS based server [1]. One of the key side effects of needing a server is that there is a more involved distribution + installation process. You just can't run it on a static server like github pages or as a browser extension.
I'm not sure if this is actually accurate:
1. https://github.com/elastic/kibana/search?utf8=&q=React
2. https://elastic.github.io/eui