I believe the IEEE and others also would come under the exceptions to the "almost" - anything you'd have to make a special effort to seek out and purchase.
> Don’t let people bully you into thinking that just because something is complicated, it’s impossible.
> This is because almost every standard (except ISO8601, whatever) is just a file, and you can read it.
In context, (my interpretation is that) "standard" includes things like The Time Zone Information Format [1], the GNU docs about TZ [2], etc. I think the idea is to say "the documents laying out the details of complicated things are still just documents, you can read them if you're interested and don't have to just see them as meant of domain experts. Some of them have barriers to access like the ISO documents, but even excepting those you have direct access to most everything you might want to understand, don't let the idea of standards intimidate you."
[1] https://www.rfc-editor.org/rfc/rfc8536.html
[2] https://www.gnu.org/software/libc/manual/html_node/TZ-Variab...