Approximately speaking, yes, that's right.
In the Personal Food Computer version 2 design, there are sensors and relays (actuators) connected to the Arduino, and the Arduino is connected to the Raspberry Pi. The Raspberry Pi runs software called ROS (Robot Operating System) that reads sensor data from the Arduino and sends instructions back to the actuators.
For example, if the air temperature sensor says it's getting too hot, ROS can tell the Arduino to activate the actuators for the air chiller and fans to reduce the air temperature.
It's complicated, but the best way to start understanding how the system works is by reading the code at https://github.com/OpenAgInitiative/openag_brain.