"For humans" is surely intended to be the opposite of "for computers". It's meant to say "When we designed this thing, we made it a high priority for it to be easy to learn, easy to remember, and easy to use".
There's certainly an implication that other libraries are designed without sufficient attention to human factors, and maybe that's kinda rude, but the same goes for making any positive claim. "A library for efficient high-precision computations": are all the others inefficient? "A flexible and powerful tool for retrieving structured data from web APIs": are all the others inflexible and weak? "A standard-conformant C++ parser": are all the others broken? (None of those examples, so far as I know, are from real projects, but clearly they all could be.)
I also find the "for Humans" thing annoying, but not for the reasons you list. The examples you list are all specific and informative. In the case of "for Humans" what is probably meant is something like "straightforward" or "simple". The thing is, there isn't anything that is NOT designed "for Humans", so the label is meaningless, IMHO.
There's certainly an implication that other libraries are designed without sufficient attention to human factors, and maybe that's kinda rude, but the same goes for making any positive claim. "A library for efficient high-precision computations": are all the others inefficient? "A flexible and powerful tool for retrieving structured data from web APIs": are all the others inflexible and weak? "A standard-conformant C++ parser": are all the others broken? (None of those examples, so far as I know, are from real projects, but clearly they all could be.)