You are right, the temperature accuracy is ± 1°C (0°C - 40 °C) and ± 2°C (40°C - 50 °C), so Galaxus' desciption is wrong.

Accuracy here means that the temperature shown on the display could be off from the real temperature by +/- 1 degree Celsius (or +/- 2 degree Celsius if the actual temperature is between 40 and 50 degrees Celsius). It has nothing to do with the fact that the display shows decimals.