I think either the simple past or the past continuous can be used in both the question and the answer. The difference, I think, is in the frame of mind of the speaker, what aspect of time the speaker wishes to stress. Using the simple past simply indicates that something happened, that an action started and was completed in the past. The person using the past continuous, however, is emphasizing what was happening in the interval between the start and completion of the action.

Real conversations don't follow the textbook! True, the answer did not suit the question exactly, but it hardly deviates enough to cause confusion.