פירוש על עבודה זרה 138:3

If the mishnah had taught only the case of the wagon or ship I might have thought that in that case the non-Jew is afraid that the Jew will sneak up on him and therefore he would not drink the wine. But if he’s left in the shop, the non-Jew could lock the door and do what he wants. Therefore, the mishnah had to teach that in both cases the wine is permitted, again, as long as the Jew does not inform the non-Jew that he is leaving.