That post reads really weird: Isn't hapi purely server-side and React purely frontend, so they can't really have replaced one with the other, but just changed the backend tooling at the same time as they changed the fronted?
No, react is not purely front-end. You can do server-side rendering (SSR) with react[0]. It can replace a view engine such as ejs or handlebars.
The article mentions that the HTTP framework "hapi" was replaced with "spife".
So yes, they changed the backend and the frontend at the same time.