Uh... no.
"Window 8.1" is an arbitrary name from the MS marketing department given to the third revision to the Windows Vista code.
Windows NT 4.0 in the late 1990's was the last Windows OS to have it's actual version number as a part of its name. After that, Microsoft decided that product branding was too important to be left to mercy of the developers. So:
- Windows 5 became Windows 2000.
- Windows 5.1 got the XP label - at that point they just seemed to be pulling letters out of a hat.
- Windows 6 was Vista.
- Windows 6.1 was named Windows 7 - god knows why.
- Windows 6.2 continued the masquerade as Windows 8.
So, version 6.4 is now Windows 10? Well, why not? It's a bit late in the game to start pointing out that the product names make no sense.