This is their answer from the wesbite Q&A
Q&A
Is it true that caffeinated beverages can help keep me hydrated?
While older studies show that caffeine can have a mild, short-term diuretic effect in individuals who do not normally consume caffeine, more recent studies have shown that this is not the case for people who regularly consume caffeine. As a result, a report on water needs released in 2004 by the Institute of Medicine of the National Academy of Sciences concluded that all beverages, including those with caffeine, contribute to hydration.
so basically, for those regular caffeine drinkers you're staying hydrated!
I can't believe this site.