That's definitely better than "go fuck yourself". "If you don't have something nice to say, don't say anything at all" and all that.
Tbh, I've seen the "go fuck yourself" attitude in almost every Free Software community I've spent time around. It's really just a matter of whether it's encouraged, tolerated, or actively rejected by the project maintainers and influencers.
I would hope that someone writing a blog post this positive would be one of the "actively rejecting" folks, but I really don't know anything about Guix (hadn't heard of it until this post).
I will say that I run NixOS on my primary home server, and while there's definitely a learning curve there, the community I've experienced is largely very helpful, friendly, and positive. Now that I've got most of it working the way I want, I don't see myself moving to something else any time soon (it's absolutely rock solid).