Grabbed from the web and explains it much better than I could!
The more common reason that dried fruits will usually have more calories and sugar is because the dehydration process removes so much of the water normally found in the fruit. That missing water would normally make the fresh fruit larger than the dried fruit, so there would be more pieces of dried fruit in the same serving size. For example, one grape has seven calories and one raisin has seven calories, however one cup of grapes has about 60 calories, and a cup of raisins has over 400 calories. This doesn't happen because the raisin company added sugar, it happened because without the water, the raisins take up a lot less space. More raisins fit into one cup so that means one cup of raisins has more sugar and calories than grapes.