I don't suspect the car is reading the temperature wrong. It's more likely reading the temperature within 1-2 degrees of wherever the sensor is placed. This can be very different from the air temperature at times. Cars typically have some basic logic to minimize the error, but they all do this differently and its always an estimation. Some ICE cars hold the last reading from shutdown until the coolant temp drops below a certain value, since they know the hot engine is going to screw with the reading until it all cools down. Often the response is slowed so you don't get wild spikes, but you also don't get a true reading until some time has passed. If you put a thermometer outside in the sun, it will read higher than the air temperature. This is not an invalid reading, its just telling you the temperature of the thermometer itself. There's really nowhere on a car you can put a sensor to get perfect air temperature readings, its a ballpark unless you're driving for a bit at decent speeds. If the car is parked, has been parked recently, has surrounding heat sources, or is moving slowly, it will be wrong. I don't see what Tesla can do about this other than just 'adjust' the reading. And then when its not in sunlight it will be reading low. They probably could get some advanced adjustments based on assumptions and other sensor data. But this is just a guess and it will still be wrong. I'm guessing they're just displaying the buffered sensor reading. Most cars are not very accurate. I'd guess Tesla has a very crude filter on the readings that hasn't been optimized. It's very likely they're well aware of this.