It seemed more like the following, to me:
Let's create a version of Windows that is aimed aggressively at tablets. None of this Windows 7 Tablet PC edition, rather something that really embraces new hardware and technology. Full pane applications and home screen, with application lifecycle management and an app store, just like other tablet operating systems.
Oh and for added value, let's allow Windows desktop apps to run on it. Users can plug in mice and keyboards and it becomes like a small desktop.
Microsoft had already designed the Start screen, but it turns out telemetry data suggests the Start menu isn't of huge importance. And Fitts's Law suggests the Start screen might actually be better in some ways.
Of course, all that is true, and is great for a tablet-first OS. But then they branded it Windows 8 (not Windows Tablet or something like that) and marketed it as the successor to Windows 7. So, in my mind, it's a marketing screw-up and Windows 9 was always in the backs of their minds as the true successor to 7.