Having finally got MultiECUscan working I noticed a whole list of sensor readings, including air temperature.

It was around 10C today so that seemed believable but I wondered where about the sensor was.

Is this measuring the temperature of the input air to the engine?

Or is there a little external temperature sensor hidden somewhere?

The MAP (manifold air pressure) sensor also contains an air temperature sensor. With these two the ECU can calculate the air mass per second and adjust the amount of fuel injected.