The person I replied to specifically said

Therefore, in technical discussions, I use the word “Linux” to refer to the OS, as “this software is compatible with Linux”. But, when I want to stress out software freedom, given a large influence of the GNU project, I say “GNU/Linux”.

So they use GNU/Linux to refer to any open system

So calling those which are just as open but not associated with GNU GNU/Linux is disingenuous, despite the influence of the GNU organization

There’s quite a few Linux distributions or whatever you want to call it that aren’t associated with GNU or are not based on GNU software

It’s not more accurate with distros like gokrazy, alpine, or chimera which aren’t necessarily based on GNU software (the last of which specifically advertises itself as „non-gnu Linux”)