Does the Wiser Radiator Thermostat measure temperature the same way as a Wiser Room Thermostat?

No. The Wiser Radiator Thermostat due to its location (next to a heat source) and design (when used without a room stat) is using its temperature sensor, but then applies an algorithm to estimate what the centre of the room temperature is, based on the above factors.  This is the temperature you will see being reported in the app for whichever room the radiator thermostat is assigned to. 

The main difference is that the Wiser Room Thermostat measures the actual temperature of a room, whereas the Wiser Radiator Thermostat gives an approximate temperature. If you find that a rWiser Radiator Thermostat is consistently too warm or cool compared to expectations, then the best resolution is to adjust the set-point (down if too warm or up if too cool).