Why they published it like this is beyond me, however. The whole point of autotools is not making your users install them (unlike CMake and virtually every other build system for C there is).
No, parent answers the question, "What is the difference between the git tree and a dist tarball?" Which is self-evidently (and unhelpfully) "you don't need autotools installed with the dist tarball". My questions are: Why does this difference exist? Why would you not track everything necessary to build a library in git? How is the dist tarball built differently than just zipping the current git tree?
"It" in my post referred to the Rust cargo package in question. The package ships configure.in, but not the generated configure. You do need autoconf for configure.in -> configure. Similarly, it ships Makefile.am, but not the generated Makefile.in for use with configure.
Note how I said "The whole point of autotools is not making your users install them".