Its called "The latent heat of vaporization" (not to be confused with "The latent heat of fusion" which is why Pluto's surface is dynamic) when the carburetor vaporizes the fuel, if there's moisture in the air, it condenses into ice. Frank actually does a pretty decent job describing it in an old video.
Anyway, carb ice is primarily about temperature and Robinson considers carb icing conditions to be from " -4°C to +30°C with the temperature/dewpoint spread less than 15°C".
With carb heat assist "technically" you're supposed to be able to set it in a hover, then forget it, but,...I never trust memes, lol.