This video has two problems.
1) Most of the people who see it do not understand or appreciate interpretive dance. PERIOD. In order for that to be understood and appreciated we would have to value it here. We generally do not as evidenced by our curriculum choices in schools today.
2) The US has always had sexual hangup issues with prepubescent to teenaged girls. If you want to understand why people are freaking out, just remember that the Olson twins, Miley Cyrus, Raven-Symone and Ariana Grande all once had large adult male fanbases who were openly titillated by these (at the time) pretty but horribly underaged women doing asexual things. There used to even be sites that counted down until it was legal to have sex with them in a least a couple of the above cases. And more than a few guys would say things that one would find pretty disgusting to read even if the woman fantasized about were an adult. And they were all at the time children, some pretty freaking young.
This is not the fault of the video, this is the fault of our society. We have our own screwy hangups with things and then we place those hangups on videos or performers or events and we justify the madness by elevating momentarily the REAL victims of our hangups (in this case victims of paedophilia). In this case Sia is left apologizing not because her work was bad, but because people have conflated it with sex with children and in doing so have hurt real victims all over again.
In summation, we have work to do as a society.