That figure is "Weekly Downloads", not in total. None of them had updates in less than two months. Also, React has published 10x more versions than Redux. So if anything, Redux might be more popular than GP assumed.
My estimates are primarily based on NPM download stats for React, Redux, and React-Redux, as well as more anecdotal evidence like "what libs are you using?" polls that I see on Twitter and such.
These are all obviously _very_ imperfect proxies for actual usage stats, but they're all that I see available to work with.
FYI my last attempt to estimate "React state management market share" was in a Reddit thread earlier this year, with download numbers and caveats included: