Which leafy vegetables have carbs? Are you talking about fiber? Most leaf veggies like spinach, kale, greens don’t have hardly any carbs at all.
(Maybe we should think of a word that means "carb that the human body can efficiently convert into glucose or fructose" and try to spread that new word. "Insulinogen"?)
yes, because they consists of 90%-95% of water, then if you cook them, water evaporates and you get some amount of carbs.
But leaf veggies is one side of spectrum, with refined carbs on another, there are bunch of stuff in between.