Commentary for Avodah Zarah 139:7

The Jew leaves the ship because it is Shabbat and does not take his wine with him. Rava assumes that the non-Jew does not know that the Jew will be away all of Shabbat, so he will not touch the wine, afraid that the Jew will come back any moment. The principle here is the same we’ve seen before. If the non-Jew is afraid of getting caught, he will not touch the wine.