The Mishnah (on the previous page) makes a distinction on squeezing fruit for juice. This forbidden as form of “threshing.” However, Rabbi Judah allows it if the juice flows naturally, so long as the fruit is edible by itself – i.e. dates which are eaten, the juice is incidental. However, if they are used as a fruit juice, i.e. dates which are used as honey, the naturally flowing juices are excluded.
The rabbis discuss which fruits fall into which category. Among the fruits discussed are pomegranates. Now since they are primarily eaten, it would seem that according to Rabbi Judah their juice which came out naturally on Shabbat should be allowed. However the text notes that:
the household of Menasia b. Menahem used to express pomegranates.
R. Nahman said: The halachah is in accordance with the household of Menasia b. Menahem.
Was then Menasia b. Menahem a Rabbinic sage (tanna)?
Does Menasia b. Menahem represent the majority of people?
Who decides matters in terms of how the practice unfolds. And is accepted.