No doubt needing to explain why they can label beers such as Style Free and Blue Label as zero sugar while they still contain carbohydrates, this special page lays out the definitions for the different carbohydrate categories.
炭水化物 (tansuikabutsu) carbohydrates plus fiber
糖質 (toshitsu) carbohydrates (alcohol, long chain sugars, short chain or simple sugars)
糖類 (torui) simple sugars (mono- and di-saccharides)
The zero sugar refers to the third category simple sugars. This includes most sugars of popular concern such as glucose and fructose. I doubt most customers are interested in this degree of detail, but it seems reasonable to me.
Photo is a web capture for explanatory purposes, copyright belongs to the company.