If you've never been in the Linux world, can certainly see how this is confusing.
This announcement is for the Linux kernel. The different Linux distributions (Ubuntu, Redhat, etc.) all bundle different versions of the Linux kernel and umpteen number of packages around that to create a cohesive Desktop or Server experience.
The kernel is the one core, similar piece between ALL of the distros. It is the desktops, package managers, etc. that differs between the distros.
Linux is an operating system kernel, the most basic layer of software managing the system and talking to your hardware. Linux exposes a standardized interface to the so called 'user space', where programs like Chrome or Apache etc run.
The Linux kernel is important, but only a small part of a whole operating system - it's the lowest layer, but there are lots of layers on top of it, including all the programs that the average user uses.
Ubuntu, Red Hat, and other Linux _distributions_ bundle a Linux kernel, common software packages, and utilities to manage these together. So there are many Linux distributions, but only one Linux kernel.
Ubuntu/Fedora/Arch/etc = Linux + lots of other stuff, without which the kernel is pretty useless (command shell/interpreter, GUI, command line tools, etc.)
Linux is just the kernel and all different distributions (Ubuntu et al) are based on it.
Think of it as if the Twitter Api was the kernel and all different clients like Twiterrific or Tweebot were the distributions (Ubuntu, Fedora, etc...). Distributions are implementations of the kernel with lots of extra features and improvements.
