Microsoft is not quick to recognize that other operating systems exist besides Windows 8.1, so its website says that you are running Windows 8.1 no matter what operating system you are using.
It will be a cold day in hell when Microsoft is held in high regard by the Linux community, and the main reason for this problem is the arrogance that it displays every chance it gets.
A Reddit user has discovered that, if you access a Windows page that shows you what kind of operating system you are using, it will always display Windows 8.1. Even if you access the website from an Android or iOS device, you will get the same answer.
This is a very small problem, which shouldn't bother anyone, but if you are going to the trouble of setting up a specialized page on your website, you should recognize that other operating systems exist, besides your own.
The arrogance I mentioned earlier was also made apparent yesterday when a story broke out about a Windows 8 update that deleted the GRUB, making the Linux operating system on a dual-boot PC inaccessible. An easily-solved problem, but it shouldn't exist.
You can check to see what “system you are using” on the official Microsoft website.