Not especially new terminology though, they used that 'Windows S... for <x>' framing for the original unix subsystem: https://en.wikipedia.org/wiki/Windows_Services_for_UNIX

Subsystems are pretty old Windows tech and it's cool to finally see the Android one come back. AFAIK they started with an Android one before ditching it to pivot to WSL. I think there may have been an OS/2 subsystem for a bit at one point as well?