Twerking is shaking butts.
But definitively there is Nothing sexual on it.
What is not being understood: There is nothing sexual about it until sexuality is placed upon it.
Having not seen the film, ask this question: Are the girls doing the dance doing it for sexual gratification in some way? Probably not.
That leaves it up to the viewer. No one thinks the gif of the dog is sexual (I hope). The reason you think a twerking girl is sexual is because you are making it so. You are putting that out there. If it is not sexual to you, then you have no reason to even bring it up.
If by this time my point isn't getting through, then my point is lost. I really hope someone might think about it though instead of trying to be right through programmed societal reaction culture.