That seems like a suspiciously large bump. I could imagine a scenario where the numbers are right, though. Is Chrome OS counted as Linux? School is starting up again in many areas...
Well, it seems like either:
1) Chrome has a market share less than FreeBSD, and so is not mentioned
2) Chrome is not considered a desktop/laptop OS, or
3) The Linux numbers include Chrome.
Option (3) seems the most likely, and I have to agree that it's driven by schools. A lot of mainstream schools are starting to use Chromebooks for their students, it's almost the default school option now, I think.
If you're counting operating systems by the kernel, why would ChromeOS be counted as anything other than Linux. Sure it is a variant, but so is Fedora or Gentoo or Arch.
I don't think you should really count the operating system by the kernel. You should count it by the API it exposes. That's what really matters.
Under this system Android and ChromeOS wouldn't really be counted as Linux because you can't easily run normal Linux programs on them. Although they may use Linux under the hood, that isn't really visible to user-space programs. Android, and especially ChromeOS could easily switch kernel with no visible effect to apps. The kernel is an implementation detail.
Many people that count on Android as Linux, just because of the NDK, usually don't have any idea how little of Linux is actually exposed to developers using the NDK for app development.
Basically any POSIX like kernel with enough support for libc and libc++ would do the job.
That was my first question, where is Chrome OS counted? Is it considered a desktop or mobile OS? I figured it should be counted with the laptops, and the mobile category doesn't include Windows so laptops must be in the desktop category. Since they don't break Chrome OS out on its own, I assume it's counted as Linux.
Even then, there's either way more chromebook-using students than I'd have ever guessed, or there's way fewer other linux users...probably a little of both.