Unix is literally the most important operating system (specification) family on the planet. Even bigger than M$ Windows. You've got all the Android phones, all the Apple iPhones, macOS, FreeBSD and all the GNU/Linux distributions. Unix-like installed base is by far the largest of any on the planet.
This was most likely posted by a kid who just thinks Unix is “old” Linux and doesn’t understand the roots of what it actually means in terms of computing.
I haven't yet read the article, but it may well be a comparison for which Linux, FreeBSD, Solaris can be united under the Unix umbrella as systems with monolithic kernels and similar conventions. Of course FreeBSD is much cooler than Linux and Solaris is much cooler than FreeBSD, but we get what we get.