I wonder what their definition of an intelligent person is? Is it a person who scored high on a test, a master of his her profession or a high school dropout who was so fascinated with Bitcoin that he got in early and now a millionaire?
Really intelligent people often are poor... Once you get rich, you get lazy because your money starts working for you and people around you constantly feed you with false confidence and optimism and this makes you even lazier.
The smartest people I know are all poor in terms of wealth but sometimes they have high incomes.
Intelligence is not a single thing because there are many different types and almost no one is good at all of them.
There is emotional intelligence, reasoning ability, critical thinking, communication ability, spatial reasoning skills, mathematical ability, subconscious reasoning, etc...
Most engineers I know have trouble reading facial cues when interacting with other people. Also they don't realize when they are being manipulated and they are incapable of manipulating others to get what they want.
People who have high emotional intelligence can essentially read the other person's emotions while they're talking to them and they can use the feedback to adjust their speech to make it more convincing. I think that's definitely a form of intelligence and it requires a lot of practice as well as natural skill.
I've met some very uneducated people with very high emotional intelligence.
They are if they made their own money. But there's no correlation between intelligence and inherited wealth.