I believe there have been a couple of studies on how smart poker players are. However, none of them have indicated poker players are smarter than any other section of society.
You have to be intelligent to apply yourself mentally to many aspects of life, but predominantly many are drawn to poker initially for the gamble. That interest in
gambling will attract all types, and yes, to succeed the game needs to be treated intelligently, but barely a session passes without some display of less than intelligent play.
In fact the longer I play, the more I pose playing on an intelligent level can be a draw back at times. I feel people get caught up in theory and tend to constrict themselves (I can/do) whereas others play with a casualness and abandon which can bring results.
So some great players are no doubt intelligent and others posses a certain boldness which has little to do with smarts.