There are 3 parts to the Hive thermostat.
1. The receiver is simply an electrical on/off switch that has the wiring connected to it. [Two on/off switches in the case of the dual channel version]
2. The thermostat is what actually does the controlling. It also measures the air temperature where it is located and then sends instructions to the receiver to switch the heating on or off.
3. The hub allows remote access to the thermostat control settings via the internet. However, items 1 and 2 will still work in 'standalone' mode for local control only without the hub.
So you are quite right, and as per @ianmcd
the receiver is useless without a thermostat to tell it what to do.