The difference is that a "react server" can actually render the dynamic react content. I don't know of a way to do this in django, unless you are able to run javascript code somehow. If you do this, you are kind of making your django app a "react server" though, since it renders all of your react components.
What usually happens in a react app is that the server delivers static content (html, js, css). When everything is loaded, react starts working on the browser and renders / fetches data.
If the server that delivers the html doesn't just deliver a static page, but actually fetches data and renders it first, the browser can instantly display the data and react is smart enough to know that it doesn't even need to do a new render, because the components are already rendered to html.
What usually happens in a react app is that the server delivers static content (html, js, css). When everything is loaded, react starts working on the browser and renders / fetches data.
If the server that delivers the html doesn't just deliver a static page, but actually fetches data and renders it first, the browser can instantly display the data and react is smart enough to know that it doesn't even need to do a new render, because the components are already rendered to html.