Take Lisp as a perfect example, I doubt you'd find very many people who think that you need to be strong at maths to learn Lisp. I wonder if this misconception came about because of Haskell's (unfounded) reputation of being a "scary abstract maths language".
When does this misconception disappear?
You don't need to be good at math to use functional programming. It's nice that there is a correspondence between math and FP, but it's mostly irrelevant when coding. You could as well say you need a FP background when learning math. Both statements are nonsense and usually spread by people who mostly read complicated blogposts instead of writing actual code using FP.
FP just offers a nice bunch of intuitive and predictable ways of processing information.