The actual article is a bit shallow on detail, but here's my interpolation...
Infra-red is quite a broad bit of the spectrum. It starts at about 800nm as light we can't quite see, and security cameras use this band with an infra-red illuminant. If we go down to about 2000nm, we are into the mid-band where some IR cameras operate. These can see hot objects but cannot people by their radiated body heat. There is a gap at about 3500nm where water vapour absorbs and emits, and cameras do not work well. Then there is another band at about 7000nm where the thermal cameras that can pick up body heat work. The cooler you are, the greater fraction of long wavelength you emit. (NB: if the exact wavelengths are important, please check as I am typing this off the top of my head).
Most black paints absorb all infra-red wavelengths equally. Some white paints will absorb the far-infra-red. What you want, and what I think they have done is to make somethng that reflects down to 2000nm, and then absorbs beyond about 400nm. This will reflect a lot of the heat from the sun, but will still radiate the heat from the building.
Does it work? Will it still work when it is dirty? I don't know, but at least it does not violate any thermodynamic principles.