Temperature is measured from the inside of the Smart-Part of your Airlock.
It indicates the ambient air temperature around the Airlock.
The temperature sensor is located inside the splash-proof sensor.
When the Wifi-chip inside works hard (for example during the first time setup of the device), heat is generated, and the initial measurements will be high. After 20 minutes of normal operation, the temperature will settle at a reliable measurement.
If you are fermenting in a fridge or another cooled environment, you will notice how the ambient air in the fridge oscillates around the set-point when your fridge turns on and off the cooling system. It takes time to change the temperature of several gallons of beer, so the beer will not be affected much by these oscillations. If you are using an external controller to control your fridge, you may be able to use the ambient temperature data to tune the controller.