Yes, the author appears to have left out that key piece of information. My understanding of CO2 warming theories are that CO2 absorbs longer wavelength IR radiating from the earth and re-radiates half of that power back to the earth. I wonder if the author is trying to point out that the extremely low thermal mass of the trace amounts of atmospheric CO2 mean that all of the energy absorbed by the atmospheric CO2 is radiated away at night and thus the average temperature of the CO2 is constant over a 24 hour period and thus cannot provide a heat affect over an extended period of time.
CO2 absorbs electromagnetic radiation in a number of wave lengths across the visible and IR spectrum and converts that energy to kinetic energy via a number of molecular vibration modes. The kinetic energy is then dissipated and transferred to the atmosphere generating an increase in heat.
Many of these CO2 absorption wave lengths overlap with the absorbance bands of water vapor and water vapor totally dominates the energy absorbance over CO2 in that segment of the spectrum.