I suspect what the authors are presuming is a relationship between the variable "proportion of workers thinking about quitting" and the variable "near future quitting rate".
Imagine if I told you that the number of people "thinking of buying a Tesla" had gone up dramatically. Now, most people can't afford a Tesla, so no, not everyone is going to buy a Tesla. But if overall the proportion of people thinking about it went up, you wouldn't be surprised if the number of Tesla sales went up soon, and would probably be surprised if it fell.
What I'm saying here is that it would be weird if those two variables are completely independent.
But that's kind of the point - the article is not saying that the proportion of workers thinking about quitting has gone up dramatically. They're saying that "25% to upwards of 40%" are thinking about this, but it seems a completely reasonable rate even in normal conditions, for all we know it may not be an increase at all.
Imagine if I told you that the number of people "thinking of buying a Tesla" had gone up dramatically. Now, most people can't afford a Tesla, so no, not everyone is going to buy a Tesla. But if overall the proportion of people thinking about it went up, you wouldn't be surprised if the number of Tesla sales went up soon, and would probably be surprised if it fell.
What I'm saying here is that it would be weird if those two variables are completely independent.