The way he's using Github is as a basic host, he could move to a different service and the blog would look the same, the URLs still work, and the visitors couldn't tell the difference.
That's day and night compared to publishing on Facebook or Medium.
(author here) Good point, but I still believe it is much better to use your own domain and have control of the whole html. Sadly because of the infrastructure currently available there is a balance between usability and centralization (but I don't think it needs to be this way). In the end, github page is being a commodity service, I could easily replace with any major provider to host the same website and users wouldn't even notice. If I wanted to be extremely radical I could host it on my personal machine on my house, but latency and availability would suffer. If I used a service like CloudFlare to improve it, we are back to centralization. Sadly, there isn't a black and white answer here.
That's day and night compared to publishing on Facebook or Medium.