The temperature sensors would be measuring the temp of the sensor chips within the ISIS box, not an external or ambient temp.
Why not measuring the outside ambient air? The surrounding air is the most important game of all to measure -- ambient air ultimately is controlling everything else in the flight envelope.
Physics of air change quite a bit with temperature, and ambient air temps change at a very high frequency in some cases at Mach 0.8 - especially in the Equatorial zone.
Semiconductor chips are pretty good at measuring themselves. A patch of calibrated diodes somewhere on the chip and a mux into a ADC is all one needs for zero-pincount internal temp precison measurement, suitable for whatever corrections might be desired for precision calibration. Pins are more valuable than gold on most chips.