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Maybe it's because he uses gentoo?

I'm not cool enough for gentoo.

There's Manjaro and few others too.

Could be openSUSE Tumbleweed.

openSUSE tumbleweed is a very nice rolling distribution. The only problem is that it needs an advanced user to configure it (installing video codecs and navigating the powerful and complex installer).

Could be Debian unstable.

Could be Windows 10.

Could be FreeBSD too

Could be Rawhide.