It's marketing speak, and no one of importance to Microsoft is going to call them on it. I would imagine their line of thinking would be Ubuntu doesn't ship on tablets or phones. OSX doesn't ship on tablets or phones. What they run are stripped down and re-imagined versions of the parent OS.
Approval of the magnitude of this claim is up to the reader.
This could get into deep discussions about what is an OS (versus a kernel), what constitutes the "same" OS (versus a modified version of the OS) and even what can be put in the same class as Windows.
I think what Microsoft is getting at is, OSX and Ubuntu don't run the same code on their mobile devices. Windows 8 will. It's marketing, and NetBSD doesn't even cross their mind.
It all depends on where is the line defining what's an OS. A Linux machine doesn't need X to be a Linux machine - Unix machines have been serving terminals for decades. So much, in fact, I joke that, in order to be a serious computer, one has to have no monitor, keyboard and mouse ports - if you really need a physical console, a serial port will do. So, I've seen Linux running programs on a very broad selection of hardware, from ARM to zSeries (68020+ has always been more of a curiosity, albeit there were serious Unix machines using them).
I mean what about previous versions of windows? They ran on tablets and desktops. If you mean non-x86 than windows NT initially was going to target MIPS and later became a x86 first(I believe they still released the MIPS version too).
Windows NT 3 could run on (some) MIPS, Alpha and PPC hardware in addition to x86. NT 4 was also ported PPC, but support was soon dropped and only the x86 and Alpha versions got any updates or support. There was even a release candidate of Windows 2000 for Alpha (I think I still have CD somewhere), but it never got a final release.
Approval of the magnitude of this claim is up to the reader.