More CO2 is better
Isn't the combustion a conversion of hydrocarbons & atmospheric air to carbon dioxide, water and heat?
So CO2 emissions is a direct function of the fuel consumption figure?
So if anything, a car that outputs more CO2 is better than a car that output less for the same amount of petrol. Because the car that is outputting less CO2 is burning less efficiently, and carbon monoxide, methane and other partial combustion products are worse greenhouse gases than CO2? So you really want the car to produce as much CO2 for a litre of fuel as possible.
So what does this number tell you exactly? That the manufacturer has made the car burn fuel inefficiently in order to reduce CO2 emissions and score better on this test at the expense of a higher mpg?
Better to buy the one with the best mpg and use it as infrequently as you can.