Similar correlations have been found with avocados. Avocados aren't particularly healthy when compared to other fruits and vegetables (not to say that they're unhealthy), however eating avocados correlates with better overall dietary quality.

Generally if you're buying more expensive fresh vegetables, you're probably eating that in place of unhealthy processed foods.

Indigestible dietary fiber also helps regulate "fullness." Seeing as the stomach is filled with largely indigestible fiber, instead of high-calorie digestible carbohydrates, it takes far fewer calories to feel full. The work the digestive system has to do in order to break down the roughage also helps mitigate blood glucose levels, by preventing rapid spikes.

If one were to eat just carbs, their readily digestible nature allows the energy to immediately be absorbed. However, the pairing with vegetables slows down the absorption of the carbs, by forcing the digestive system to work on the vegetables in addition to the carbs.

Now this isn't to say carbohydrates are bad, but they shouldn't make up the majority of ones dietary volume.

Seriously, though, I would expect that the biggest correlation is to ethnic/regional cuisine (particularly southwestern US and Mexican), which I'm not convinced moves the "healthy lifestyle" needle in any particular direction.