I have nonidea how one would get a circuit diagram for this. The code was just cut and pasted from the arduino web site so I'm going to assume the code is correct.It just reads the sensor and prints it to the display.
I understood that the kit's thermal sensor is mounted internally.
And that is why I think that he will not make correct measurements of the environment, because the heat generated by his electronics will affect the temperature measurements.
See page 4.
The schematic shows an HTS221 temperature and humidity sensor. The datasheet for that chip says:
Temperature accuracy: ± 0.5 °C,15 to +40 °C
Either the chip is in a warm place or the software is wrong. It's not as simple as reading the temperature from a register. You have to read the calibration values from the chip and do a linear interpolation. Maybe the library got it wrong?
If you have a fan blow room air across the board, do you get a more reasonable answer?