Are you sure it was the alcohol and not the billions of good bacteria? :-)
Different brands have different amounts of naturally occuring sugar based on the fruit juice that is added to it. For example, the blueberry flavored by the Synergy company has only 4 gms (1 tsp) of sugar in 16 oz bottle, which is really good.
Whereas, I just discovered the little 8.5 bottle by Kombucha Wonder Drink has 14 gms of sugar! Too much, in my opinion -- but still much better than straight up juice.
YOu can also get plain, don't have a bottle at the moment to check the sugar content - but probable has little to none.