Once on a Canada to USA border crossing, my group was told we had to declare all food items even if legal. Includes water, chips, etc. It was the only time that's happened to me. May have just been the way the officer interpreted the form, which lists "food" in addition to meats, fruits, vegetables, etc.

The situation in the OP is a good example on why no one should ever argue with a customs officer, even if the officer is behaving unprofessionally (which seems to be the case there). Arguing only escalates things and brings you into the problem.