They do make mention of being actively engaged on SO, but this didn't at all read like a marketing piece for getting more SO users.
The key point seemed to be one I've seen echoed repeatedly elsewhere: a lot of good developers write and share a lot. It doesn't have to be Stack Overflow.
"Good" in this context I take to mean holistically good. Not just good on purely technical skills, but soft skills(particularly effective communication), organizationally dynamic, etc...
I don't even know what kind of statistical basis they want to put their claims on. A better title would be "the great developers that you hear from a lot share a lot".
They make an effort not to promote "share your knowledge on SO" strongly, but it's one of the two actionable thoughts any developer reading this would have. "I should write blog posts" or "I should answer questions on SO".
There are good developers that are out there helping others, but that usually doesn't require tremendous skill as most of the questions are simple and can mostly be resolved by looking at the documentation.
The hard stuff usually comes from doing things that were never done before or going deep inside a system. This usually doesn't apply to many people and is hard to share.
You could share like in open source code contributions or in a blogpost in your own blog / domain