I think you're misunderstanding what he's trying to say. He's not saying that knowing finance has anything to do with being smart--if anything, it's the opposite: Of the people he considers smart, he noticed knowledge of finance isn't widespread. Perhaps the average smart person doesn't find the problem interesting enough.

For what it's worth, I was one of those people. I didn't go for my undergrad until 8 years into my adult life (I'm a veteran), but I had done extensive reading about business to the point that most of my BBA (which I was taking as a bonus alongside CS) felt like review. Except for finance. I knew the basics, but even undergrad courses revealed that my knowledge was very shallow. I think it's just something that people don't expect to have that much complexity. I wouldn't have thought to learn it if I hadn't been forced to take it in school, but I took as many finance courses as I could once I realized the knowledge deficit.

Is finance hard? The sophisticated stuff can be, but generally in comparison to engineering it's not. But nonetheless, nearly none of the computer scientists in my class or in my professional circles have bothered to learn...probably because they're more interested in compilers ;)