It's not a question of being smart, it's about education. People in rural areas tend to have less education and are more likely to have inadequate sexual education (abstinence only sex ed programs for example) than people in urban environments.
The education gap between rural and urban settings is a subject of much concern and unfortunately the tendency towards religious views has led to increased ignorance about sex as comprehensive sex ed is more likely to be rejected in rural areas replaced by "abstinence only" programs which result in higher rates of unplanned/teen pregnancy and even where comprehensive sex ed is offered, religious parents are much more likely to forbid their children from attending.
It still your bias making a blanket statement that the data you link doesn't really back up. Sure there is less educated people in rural areas, but it isn't that much less.
