It contains a theme coded specifically for the blog, with examples taken from Hugo documentation. The purpose of not taking a great existing theme is to learn new webthings (because I really suck at web development). Also I wanted to learn a bit about Bulma, a tiny CSS framework without a line of JavaScript.
Hugo is really powerful yet pretty light and really fast. I do like the way templating is used to achieve very elegant tricks. In the past we would have used databases and dynamic languages like PHP for the same result.
I think that using Wordpress for a little static blog is no longer relevant and I am really enthousiastic about projects like Hugo. Additionnally, the community seems very friendly. Other static CMS such as Ghost have an economic model that I don't like (eg you have to pay for plugins) and Grav is great but not so artisanal. The learning curve is pretty high and you're encouraged to use an existing theme with the PHP admin interface.