I assume they are also claiming to grind it lishma (with the intention that it will be used for the mitzvah) and that it's not as simple to rely on lishma by machine-made as by hand (as with regard to the remaining matzoh-making processes and printing sifrei torah).
...matzah shemurah must be prepared with the intention of fulfilling the mitzvah of achilat matzah. This means that if the cutting, grinding, kneading and baking of the matzah were done without the proper kavanah (intention), then the resulting product may not be used to fulfill the mitzvah at the seder.
This brings us to the primary objection against machine matzah: Matzah
shemurah needs to be made by committed Jews who have the proper
kavanah, and a machine could obviously have no such kavanah. The
defenders of the machine asserted that a machine was a tool, no
different than a rolling pin, and therefore, it sufficed if the Jew
operating the machine had the correct kavanah.
By the beginning of the twentieth century, virtually the entire
non-Chassidic world accepted the use of machine matzah peshutah for
the eight days of Passover. Most Chassidim continued to disagree. The
debate about using machine matzah shemurah at the seder continues
until the present day.
(from:Rabbi Shmuel Singer at OU.org; see there for a more complete discussion of the history of the machine vs. hand-matzah controversy; ; see also: http://www.yutorah.org/lectures/lecture.cfm/796575/Rabbi_Chaim_Eisenstein/Halacha_from_the_Daily_Daf:_Pesachim_40--Defining_Matzah_Shmurah_&_Is_the_New_%27Hiddur%27_of_Hand_Ground_Matzahs_Really_a_Hiddur#)