An exact quote would help; I find this interpretation confusing.  The proceedure seems quite simple to me.

If `rmdir TESTD` succeeds, then the two links `TESTD/.` and `TESTD` are removed.  So the link count of the specified directory falls to 0.  This can be verified by running a shell inside the directory and running `ls -ld` after the directory has been unlinked (removed from its parent).

Once a file (such as a directory) has no links, and no running processes with a reference (file descriptor or current directory), it will be truly deleted.

Note that link count is irrelevant to whether `rmdir` can succeed.  Creating a file in the directory prevents it from being removed.  But creating a file does not increase the link count of the directory.  The test that stops `rmdir` from succeeding is if "pathname contains entries other than . and .. ; or, pathname has ..  as its final component." (`man 2 rmdir`).