What good would carb heat be if it actually CAUSED carb ice? I agree, that story is a crock.

You're saying that the guy turned on the carb heat, and all of a sudden, the warmer air started sucking up moisture? Moisture from where??? If the air is too cold to hold enough moisture to cause carb ice, then there's also not any moisture to be picked up by warmer air! Just because warm air has the capability of holding more moisture, doesn't mean that it always does. The moisture would have to come from somewhere, and if the "colder" air couldn't provide, then where is it coming from?