Yeah... I can see why people may think it's inappropriate but I think that's because the media is so dominated by male businessmen getting women to be sexy and seductive. Music videos: dominated by barely-clothed women. Advertising: same. Modeling: same. So the whole suggestion of sex and entertainment have become entwined, and I think dance is probably the most obvious victim of that because it's very physical and flexible.
But to look at the kid in the video and think "inappropriate" is kinda just... letting the idea that she's sexualised take place, or criticising the girl for being a slut or whatever (when, more than likely, she has no idea what sex is). I don't see it as such. (I'm not saying you do

I just saw a lot of comments about it somewhere on Tumblr and found it interesting how women are so often shamed for what they wear or how they act, when it's a male gaze that's associating it with sex in the first place.