It has nothing to do with the thermal qualities of the object and everything to do with being able to alter emissivity. Thermal cameras are only accurate for a given emissivity and high end thermal cameras allow you to tune emissivity to get accurate readings [1]. By altering the emissivity of the material at will, you can camouflage your object against a camera assuming constant emissivity.

[1] http://en-us.fluke.com/training/training-library/measurement...