Think for a minute about the words “microblog” — a twitter-like presentation format limiting individual content chunks to a few sentences in length — and “book”, a longform collection of prose typically running tens of thousands of words in length.
The underlying platform of Micro.blog, the specific service sotu was asking about, is built on Hugo. If you make a Twitter-sized post, it will show up just like it would on Twitter or Mastodon or another microblogging platform; if you make a long post, you'll get a field to add a title, too, and when you read it on the timeline (and when it gets crossposted to Twitter, if you have that enabled), you'll just see the title and a link to the longer post.
I don't know how Manton made that site, specifically, but focusing too much on the terminology here may lead you astray a little in this context. :)
