their idea is to use full tech tree as a generic civ when you start (in the example of using india). then at game start you have 3 vill and TC, in the TC theres loom, and 3 other technologies you can choose. each tech represent a sub civlization and by researching that particular tech, it’ll determine which bonuses and tech/unit are disabled from the full tech tree.
thats how they do it, which technically speaking you can play on full tech tree and not to choose a sub civ.