Not OP, but I think by "(not) functionally a carb" OP means "(not) processed as carb by your body".
Functionally => how it functions, how it interacts with something else, c.f. "functional testing" :)
Unsure if this is nutritional terminology or just HN-reader terminology.
Because your body processes fructose through a different potentially more damaging pathway than glucose. It’s a carb if you like but it’s the worst carb for you by a huge margin, especially when eaten without fibre.
Isn't carb an abbreviation of carbohydrate, which in turn is a synonym of saccharide?
How come fructose is a monosaccharide but not functionally a "carb"?