Is that guy really an experienced developer? He's obviously talented but experience and talent are different things. It sounds like he has less than 10 years under his belt.
I would say someone with 5 years experience could be senior to someone with 10 years under their belt, granted the former worked on the right projects that gave them valuable experience, with some combination of design, understanding trade offs, implementation, and social/management skills managing delivery of their features or taking complexity and simplifying it (both technically and from a requirements perspective). You could work 10 years and not hit those points.
I expect someone with 10 years is hands down more experienced than someone with just one year under their belt, but otherwise, looking at how long you’ve been in the industry is kind of meaningless without understanding what it is that you did.
WinForms -> ASP .NET MVC
and then
Backbone -> AngularJS -> React
(including participating in React development) gave you the kind of exposure and experience you needed for Redux.
I think a lot of people reading on here missed this parts and I certainly didn't catch onto this reading your Things I don't Know as of 2018 post or the "Things I do Know" post you linked to.