Per the link below that explains it’s statement in the article itself “…psyllium husk, which contains no carbohydrates other than fiber, can legitimately be described as having zero carbohydrates…”
Ref: https://healthyeating.sfgate.com/carbohydrate-content-psyllium-husk-11597.html
I have started on Psyllium husk to additionally reduce my cholesterol that (I feel) increased due to Keto. Article above definitely makes me hopeful too.