I dont think that's what they're doing. They seemingly cache some common templates and then fill in the dynamic placeholders per-request. So, their new architecture that has some sort of distributed in-memory cache allows for doing so much more efficiently than, presumably, doing the same queries over the network. The way I understand it, its essentially just a fancy SSR.
Not necessarily - SSI/ESI do http requests for each placeholder and fill it with an HTML fragment. They may just be doing some templating of whatever sort, from the kv store.
