Your mistake was giving them an answer instead of asking how the scale was setup before giving them a number. Psychologically, by answering first your established that the question was valid as presented and it anchored their expectations as the ones you had to live up to. By questioning it you get to anchor your response to a different point.

Sometimes questions like this can be used to see how effective a person will be in certain lead roles. Recognizing, explaining and disambiguating the trap question is a valuable lead skill in some roles. Not all mind you... And maybe not ones most people would want.

But most likely you dodged a bullet.