Their backend is partially inside, partially outside Anvil (eg I believe the campaign management backend runs in our hosted server modules, but the compute-intensive machine learning is offloaded). And it's all under their control - it's their code!

The wonderful thing about the Uplink is that the boundary between "inside Anvil" and "outside Anvil" can be very fuzzy, because you use the same APIs. (See my "escape hatch" post above)