I have attend college myself. From my own experience college has made me smarter. It has increased my knowledge, taught me how to think, and has made me a better reader. Even though I have never did anything career wise with my college education it has enriched and helped me in other ways in my life.
People are not always smarter just because they went to college. People can be brilliant and successful without going to college, and many are. However, generally people who are college educated are smarter, because of self selection, since people who are smarter choose themselves to go to college from the population.
What college does is expand your mind. It gets you to think in ways that you haven't thought before. Of course, you can do this without college by reading, traveling, experimenting, practicing, and just pondering specific topics. But college definitely gives people an intellectual edge, whether it be large or small.
People who attended college are not necessarily smarter than other people. What college does in make people memorize and study content. This is not "smart." This is not innate intelligence. Some of the smartest people in the world did not graduate college. Bill Gates is the best and most popular case in point.
People who do not attend any form of higher education can be just as smart as those who did. But they have not put themselves into a forum where their ideas must be presented, discussed, and critiqued. That means their intelligence has not been honed and their opinions can become stuck and uninformed.