I have a coworker who I discovered a few weeks ago had no idea internal monologues were a thing. I had to explain that it's a real documented phenomena and that it's actually a minority of people that don't have one. She's pretty damn smart, too. I also play D&D with a guy who has aphantasia. He's also pretty damn smart and you would have no idea he was incapable of visualizing things if he didn't tell you. Him casually mentioning it in conversation surprised people who had known him for years. So, yeah, absolutely no correlation between intelligence and how your thoughts may or may not produce phantom sensory input.