Never been asked regarding a suitcase but have been asked when it's a cardboard box. I was honest and said furniture to which they tagged the boxes and had no issues or follow-up questions. I am guessing it may be SOP for the agent to ask when the item is not a typical suitcase or piece of luggage.

I really miss the days of setting two boxes of twelve pack bottles on the TSA belt for X-ray and then carrying them on board and securing in the overhead bin. Made several beer runs from DEN during that time.