It's kind of making me laugh to think about girls wanting to wear shorts with decorations on the seat. It reminds me of the ruffled panties my mom used to make me wear when I was really little; they had ruffles and lace across the tush, and were meant to show under the short dresses that little girls wore in that era. (I just gave my age away, didn't I, LOL!) I was forever getting caught wearing them backward, because if the decoration was supposed to be for me, I wanted to wear it where I could see it!
Finally, my mom explained to me that the ruffles were not for me to see, they were for everyone else to see, that it was supposed to be that way. It sounds to me as if these shorts are a modern take on the same principle; regardless of the age of the wearer, it is not the wearer who is meant to see those decorations. Is it sexual? Maybe, maybe not, but it is obviously meant to attract the attention of others.