SSR means server-side rendering. String-ness is irrelevant (everything is a string as far as HTTP is concerned). The difference is between serving HTML vs JS for the purposes of generating a DOM tree. The article is using nanossr specifically to server HTML, MPA-style. My thing is using template string, which is what systems like lit-html use for their flavor of "declarative components"

Whether one wants to squint at this and think of React is neither here nor there, IMHO. Svelte, for example, cannot implement this website in this MPA format with only one `.svelte` file, but I don't think it's necessarily more verbose or slower to develop with than, say, Gatsby.