My air intake temp is dead on at cold start and starts to be off as the engine warms up. I checked escapingoth's about a month ago and it was exactly the same as mine.
I assumed that the intake air simply gets heated before getting in the engine (or close to the sensor). The more you open the throttle the closer to outside temperature it will get.
21C in garage, 21C outside
Iddle Cold: IAT shows 21C
Iddle HOT after 5 minutes: IAT shows 32C
Riding highway shows 26C
Climbing a hill, 20% Throttle IAT shows 24C