He's right though, SteamOS was triggered the first time around by windows 8 and the associated store and surface rt launching as a "store only" device, widely considered a harbinger of Microsoft trying to get their whole ecosystem to be apple like (in house hardware design with software distribution platform that gives them a cut of everything).

When they came up short, they tried Windows S on x86, thinking that a Windows that could run fewer applications would somehow be seen as more valuable to customers because "security".

I think they have learned their lesson, again, that long reaching app compatibility is the only reason their OS has a hold on the industry, but around window 8 release it was abundant clear they wanted to lock down the platform apple style. I recall at the time Valve said as much when they tried SteamOS and steam machines and pushing developers to do Linux versions. It was a flop then, but Valve ultimately revitalized it with Proton and the Deck.

Let's have an extra source then:

https://www.zdnet.com/article/valve-windows-8-is-a-catastrophe-for-pcs/