The comic just points out the irony of buying into the personal responsibility narrative while participating in the hyperconsumption which is the real driver of pollution.

Therefor it still works imho, because the car is a ridiculous toy for rich people and stands for over consumption and over production due to capitalism. And the whole carbon foodprint thing was a PR stunt by the fossil fuel industry to shift the narrative away from the systemic issues towards individual responsibility. Obviously the bottle cap is not about the carbon foodprint at all. It is to reduce plastic pollution. But imho that confusion makes the joke even stronger because most people gobble up those pseudo-band-aid solutions to real issues without questioning their effectiveness in the slightest.