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 ;)

I'm not sure what you're trying to get at...are you trying to say business people are smarter than OP gives them credit for?

"I very quickly realized that" <- Implying a prior assumption that was proven false

"very smart people" <- The set of very smart people OP has met, which hinges on perspective

"often" <- The key phrase here, implying that it is generally (but not always) true

"have very little knowledge of finance and business." <- The assumption at hand

I'm assuming OP thinks of STEM people as the definition of "very smart," based on his description of his degree, and his feelings about coding. OP may have assumed that since his knowledge is comparatively trivial for STEM people to learn, the knowledge might be widespread among what he thinks of as smart people, and was surprised when this valuable knowledge wasn't. In my experience, the average kind of person I'm assuming OP would consider "very smart" is either averse to business, or didn't bother learning business because it took time away from the hard problems they were more interested in, even though they easily could have.

More generally, the total set of obviously and profoundly smart people is bound to be (much) bigger than the set of obviously and profoundly intelligent people with knowledge of finance. Are there smart business people? Absolutely. But it's probably a small percentage when compared with the total set of Very Smart People. Also, at least in my school, the smartest people tend to go into harder disciplines, so that may further dilute the numbers of finance knowledge among the pool of Very Smart People.

So, there are multiple ways OP's statement can be true without being specifically about the capacity of intelligent people to learn finance through study or experience.

Yes, this what I meant: "OP may have assumed that since his knowledge is comparatively trivial for STEM people to learn, the knowledge might be widespread among what he thinks of as smart people, and was surprised when this valuable knowledge wasn't." Sorry for the confusion.