This source only includes the carbon footprint of CO2. Other greenhouse gases : CH4, N2O, F-Gases are not taken into account here. CO2 represents 74% of global greenhouse gases emissions, hence on average the carbon footprint of all greenhouse gases should be about 35% higher than the CO2 carbon footprint.
The carbon footprint of a country is the total amount of CO2 produced directly and indirectly by this country. It's the sum of the territorial CO2 emissions, plus the CO2 embedded in imports minus the CO2 embedded in exports.