That doesn't fix the issues mentioned. (Whether it's an "alternative" stdlib for C is debatable; nobody ever said that glibc is "the" stdlib for C…)
It is the de facto standard on Linux.
That doesn't make it the official implementation of ISO C, just one among many.
Which Linux? There are plenty that use MUSL instead.
musl is just another implementation of the true stdlib. I think what they want is an alternative to standard-conforming stdlibs that fills a similar niche - in other words, a "non-standard" standard library.