The more I think about it, this was written for marketing purposes. He doesn't really make a point. It just draws more attention to the product.
As for non-free I find it awkward since most of the time one would have to bend over backwards to support it (e.g NixOS with steam) or adopt external package management systems (Snap, etc) which only add complexity. It also reduces trust as we can't verify builds are in fact not tampered with and so on. If we avoid snap, nix, and guix for packaging then we must rely on upstream updating to ensure it won't break upon the next upgrade where we could have just compiled otherwise. This is inconvenient.
So, in my view I find it positive that there is a push for companies to open source when supporting GNU/Linux as it creates a much better experience for package maintainers, users, and the company involved while increasing the general reach of FLOSS software to other platforms (BSD, Plan9, ..).
Quotes: “This is going to be a very hard sell being a proprietary closed source system to Linux users, many use Linux because they have bought into the idea of open source. Good luck with it anyway” “If it were FOSS, I would have downloaded it and compiled it 20 minutes ago.”
Is that it? The rest of the thread seems pretty mild and politely interested. This was two years ago and I think I'd be over it by now.