I never claimed it was a GNU project, I said it was a standard library for GNU Make. And it's been around for 19 years at this point, so I feel like the FSF has had plenty of time to come to me and ask me to change the name.
But then it's not really a standard library, is it? A standard library is the set of libraries that's shipped with the language/compiler/interpreter/runtime; it is specifically the batteries that are included. If a library has to be separately added, then by definition it isn't standard. Ex. Boost is a very common C++ library, and people could reasonably argue that it should be folded into the standard library, but it isn't the standard library, and nobody's calling it that except in an informal or joking sense.
I don't think your definition of "standard library" is correct.
For example, there's glibc (which you might argue "ships with" GNU stuff) and then there's musl (https://en.wikipedia.org/wiki/Musl) which is an alternative standard library for C programs.
This morning I shot an elephant in my pajamas; how it got into them, I'll never know...
If there is a standard library for GNU Make, one would expect it to be part of the GNU project.
That the GNU project enforces a certain naming convention on projects doesn't oblige you in any way to avoid that naming convention, but adopting that convention when you are not part of the GNU project creates confusion.
You might diffuse/disclaim the confusion up front. I notice your github repo has three archive files, no license, and no readme.