I disagree. I think that if you understand functional programming and abstraction, you understand a certain amount of Category Theory even if you don't know to call it "Category Theory".
Analogously, "you don't need maths to tell you that one and one is two."
As soon as you have an understanding that one and one is two, you have maths.
That's bait and switch. The question is whether people should study category theory to be better programmers. Not whether good programmers have intuitively mastered some category theory.