Color temperature is a representation of the shape of the spectrum as compared to a blackbody of the same temperature. It is not necessarily representative of t

Color temperature is a representation of the shape of the spectrum as compared to a blackbody of the same temperature. It is not necessarily representative of the surface emitting the light. Because the moon absorbs some of the wavelengths of light more than others it shifts the spectrum to represent a blackbody object of a lower temperature. So depending on what wavelengths are absorbed the color temperature can actually be shifted up or down. For another example, the color temperature of standard incandescent bulbs is ~2700K, and this is similar to blackbody radiation. However, LED lights can have the same color temperature, but the surface of the LED is not at 2700K because the light emitted is being created through a different process than blackbody radiaton. That said, I am still wrapping my head around the xkcd explanation because blackbody radiation of the moon at 100K would not be enough but there is also reflected sunlight at a .16 albedo.