Going by the analysis in the post, and in the parent comment, the 20mm would probably be positively correlated with attractiveness because it's easier to get a shallower depth of field with it.
However, you're certainly correct that conventional photographic wisdom is that people look better on longer lenses, for just the reason you cite -- wider angles can distort faces unpleasantly. It would have been interesting to see an analysis of lens length & perceived attractiveness from this dataset.
