[Kanazawa's study] showed that young adults who identified themselves as "very liberal" had an average IQ of 106 while those who identified themselves as "very conservative" had an average IQ of 95.Evolutionary psychologists certainly have a lot of leeway to explain anything that they see in the data and to pick the explanation that pleases them the most.
"The ability to think and reason endowed our ancestors with advantages in solving evolutionarily novel problems for which they did not have innate solutions. As a result, more intelligent people are more likely to recognise and understand such novel entities and situations than less intelligent people, and some of these entities and situations are preferences, values, and lifestyles," Dr Kanazawa said.
Humans are evolutionarily designed to be conservative, caring mostly about their family and friends. Being liberal and caring about an indefinite number of genetically unrelated strangers is evolutionarily novel. So more intelligent children may be more likely to grow up to be liberals.
The study is of young adults. Intelligent young adults might be liberal because they are going to better schools, and schools promote the liberal world view. What happens when these intelligent folks — and they're not that intelligent! — get a little older?
The linked article summarizes the material in the book "Why Beautiful People Have More Daughters: From Dating, Shopping, and Praying to Going to War and Becoming a Billionaire-- Two Evolutionary Psychologists Explain Why We Do What We Do." I read that book a while back. It's pretty interesting.