Apparently, PlayerUnknown's Battlegrounds (PUBG) is a massive hit in China and this results in a resurgence of Windows 7 on Steam. Windows 10's marketshare on Steam was down 17.38 percentage points to 28.6 percent in October, while Windows 7 was up 21.47 percentage points to 65.4 percent. This is because Chinese users are far from keen to upgrade to Windows 10, they're sticking with Windows 7.
But where's PUBG in all of this, though? Well, that slight piece of the puzzle you can glean from Steam Spy's analysis of PUBG's player base, which shows an adequate (roughly) 600% percent increase in player count from around 1 million players in August to around 6 million as of October. Around 3.1 million of those entered the scene starting in September. PUBG is simply a phenomenon in China, and Chinese users really seem to be trying to make the most of it while they still can: reports peg the game as being in line for a ban from the Chinese government, as a Chinese Gaming Association has deemed PUBG to go "against Chinese values and ethical norms."
The massive influx of Chinese gamers also significantly changed various other metrics in the Steam Hardware Survey.