A traveller who validly fasts from the beginning of the day and returns home without invalidating that fast simply continues and completes the fast. This is not the same as abstaining for the remainder of an already unfasted day.
Being a traveller does not make all situations identical; the existence of a valid ongoing fast matters.
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Kitab al-Sawm: Unconsciousness, Recovery, Menstruation and Abstention
A traveller who validly fasts from the beginning of the day and returns home without invalidating that fast simply continues and completes the fast. This is not the same as abstaining for the remainder of an already unfasted day.
Being a traveller does not make all situations identical; the existence of a valid ongoing fast matters.