It's trendy for accomplished people to talk down about themselves as a way to sound cute. It's similar to software developers who like to say "I don't know what I'm doing, I just Google and Stackoverflow all day." It has a certain charm to it, and certainly there are some people for whom it's true, but overall it's just a misguided attempt at being modest but ultimately a horribly misleading statement.

"Do not worry about your difficulties in mathematics, I assure you that mine are greater" - Albert Einstein

I didn’t say they can’t perform it. I’ve seen a laureate get plenty of trival math wrong. It doesn’t matter.