Valve have put out their usual monthly Steam Hardware Survey, which shows a bigger decline than usual for the Linux marketshare.
Last month, Linux was sat at 0.60%, but as of October it has dropped to 0.35% which is a sharper drop than usual. It's worth noting, that Mac had an even bigger drop.
It's easy to see why though, China is now the biggest market on Steam according to their survey. Simplified Chinese has increased by +26.83% making their share of Steam's market at 56.37%. That's a huge influx of users from that region, which can easily account for the reason Linux has been dropping recently.
When you look at it even further, Windows specifically has 57.45% (an increase of +26.99%) using Simplified Chinese as their language. Compare that with Linux, and only 0.53% (a drop of -0.11%) use Simplified Chinese. Linux just isn't popular in that region, so again, the drop does make sense and can be accounted for.
A large portion of that increase has likely been fuelled by PLAYERUNKNOWN'S BATTLEGROUNDS, which is not available on Linux and is the most played game on Steam right now. There's also rumours of it being banned in China, which has likely caused another surge in people taking a look at it.
I should remind you, that a drop in the marketshare doesn't mean less users. It likely means that Windows growth here due to the two above points has just dwarfed any possible increase in Linux gamers on Steam.
I don't see this as any reason to panic, at all. Once the hype around PLAYERUNKNOWN'S BATTLEGROUNDS starts to vanish, the numbers will likely start to even out again.