It's Virtualized Windows running an RDP session per-app, something VMWare has offered forever (Unity) and Virtual PC had too (forget what it's called).

Not a bad idea, mind - I use Unity mode today to run apps that only work on older versions of Windows.

So it's not a "Linux Subsystem for Windows" but a virtual Windows PC with a Unity-like mode, so it's as resource-intensive as any VM.

That said, I think it's great someone put it together!