Oh, the Admin ui is client-side react app. It accesses data through RestAPI requests. You can open Developers tools in browser and look at the Network tab, you will notice that it gets all the data in real time from the strapi’s backend.
That’s how you make difference between a CSR and SSR. If the web page returns all the content in javascript files/html files than it is SSR, if it requests APIs to get the data then it is CSR.