I suspect you've fallen prey to a very common stumbling block: You've conflated temperature and heat, or maybe more specifically heat and warmth.
Something is warm when it feels like it has a higher temperature than you, or than the embient environment. Heat, on the other hand, is merely the transfer of energy in a way that doesn't do any useful work. Both heat and work can raise an object's temperature.
We can take the temperature of an object by measuring its IR output because an object that is radiating IR light due to it being warm will give off a certain amount of IR radiation per square metre that is dependent on its temperature, assuming the radiation is thermal radiation. The IR light being given off by the auora here isn't caused by thermal emissions, though, so we can't tell the temperature of the gas by imaging it.
So, in this case, there's actually no direct relationship between IR imaging and temperature. On the other hand, the IR light that is being captured by the imager isn't doing much work (it does a little, as it pushes the space craft ever so slightly), so the relationship between imaging and heat is basically that the image is of heat. But that's true regardless of the wavelength of light captured in an image!