This means that the maximum voltage in that A4 input will be around 2.85 volts, as long as you don't change the 15k resistor. Even if the thermistor was replaced by a shortcircuit (a simple wire), voltage in A4 would go DOWN.
But if it was replaced by a open circuit or the thermistor shows more than 20K resistance, due to fault or temperature, the voltage would go up.