I think the reason for the correlation is cultural not genetic for example
if you are very pretty and very rich and have supporting loving family that is balanced and open minded etc.... you wouldn't be plagued with frustration or insecurity issues allowing you to more easily focus on the task at hand (IQ tests or any social interaction).
If you have body issues, self confidence issues, been a victim of prejudiced or fear it etch your mind is juggles more things - mainly negative / fearful thoughts.
emotive landscape has MASSIVE effects on performance of any kind.
When your happy with your lot things work.
Those that are more curvy would have a tendencies to think they have the "X-Factor" which is a big thing for society for women to be feel good about themselves.
So on average - they may score better when they apply themselves.
To the contrary thought - some that have body issues but high wisdom may have an ability to dispense of anyithng associated with anything OTHER than their intention (force of will) ... or what they deem their "gift" ( they may have been told they are smart )
... effectively causing higher IQ test scores.
When we are distracted or have 1000 issues in our lives we all know paying attention to something abstract is harder. I beleive that intelligence is a product of managing Attention, awareness, patience and focus and not separate from it.
Healthy body image in this culture removes some barriers effectively explaining these results.