No, this is not true. In fact and from the time they are picked, fresh fruits start to gradually lose some of their vitamin content, mainly vitamin C. Also, during the drying process of fruits, they lose almost all of such vitamin content but they preserve almost all of their content of vitamin A especially. Therefore, it is not true that dried fruits are more concentrated in vitamins but rather in sugar basically.
Also, dried fruits are an important source of minerals (potassium, calcium, iron, phosphorus, magnesium, selenium, etc.). They are also rich in fibers but have a very low water content. They are high in calories and well suited for high-level athletes or for people wishing to gain weight. In addition, and although they are concentrated in sugar, there are some dried fruits that have been enriched with sugar. Therefore, always read the labels before buying some.
On the other hand, and due to their high content in sugar and calories, dried fruit are not advised for diabetics (who must always seek permission from their doctor) or for those wishing to lose weight.
Finally, it is always advisable to consume dried fruits in moderation and to diversify their types as much as possible so that to profit the most from their benefits.