Yes, but this article is not about the GNU parts. It is about how the Linux kernel begins execution. There is nothing wrong with describing this as the "Linux (kernel) booting process".
though there is a bit of syslinux/grub stuff that isn't strictly this.
I think you misunderstand; the article originally used the term “the GNU/Linux kernel” throughout, and callesgg thought that this was odd, since the article was actually about Linux (the kernel) and not about GNU/Linux (the operating system).
The article has since been changed to simply use the name “Linux”, so I could understand that someone could become confused about what callesgg was talking about.
though there is a bit of syslinux/grub stuff that isn't strictly this.