If you ask people to rate others, and only give them one factor to go on (in this case: dancing), then of course the best dancers will be chosen. This is especially true given that popular dance is highly sexualised. (I would wonder whether they would have got the same result if they had chosen ballet or interpretive dancers.)

Essentially what they have proved is that people who are good at moving well, and in a sexual fashion, are more attractive (if this is all they are judged on) than those who are more clumsy and awkward.

This is rather akin to proving that cheese is a food.

To really prove that dancing makes someone more attractive you would have to consider all the other factors, e.g. if the dancer in question was a violently misogynistic alcoholic then it wouldn’t matter how well he moved, he would still be less so than a considerate bad dancer.