[ctrl]+f and look for powered by
or go page 17
ELI5?
Looks like a guide here for how to include steam branding, but “Powered by SteamOS” branding might be referring to Valve letting third parties, maybe Asus Ally for example, come preinstalled with SteamOS instead of Windows.
But pure speculation
Guidelines on how Valve wants manufacturers to use the SteamOS branding, implying they may be in talks for people to ship products with it pre-installed. Which may also imply they’re getting somewhat close to a release of a generic installer that’ll work on more hardware as I think I remember reading they wanted to get it to hardware vendors first
Remember the problem with the steam console was the vast array of hardware options and price points
Hopefully Valve will ensure all machines are to spec