Same organization (CBP) is responsible for both functions - no blurring of lines. My guess, the CBP Officer was attempting to elicit a response to determine if you should be sent for a more detailed inspection of your luggage. From my experiences in Customs (having seen CBP officers perform a similar procedure at both IAH and ATL in the past year to other pax), you would have been told to report to a secondary security office, escorted to the baggage claim area, then escorted to a screening area for detailed inspections.