I think since they used [todoId] in the example they mean a static page which does not exist at build time. Which both can do, it’s called ISG (or on-demand in the Astro docs), but it requires a server to work, or you can create a static route that accepts any parameters and pass those to JavaScript to run on the client.
Yeah, what the other commenter said. getStaticPaths still requires you to define the rendered routes build-time