I heard you should avoid eating food that has a greater #mg of sodium than # calories. Is this really how low a healthy salt intake should be?

Total matters. Your total sodium intake for the day is what matters, not the ratio to the total calories. Ask your doctor if you should be on a low salt diet for a specific health problem for greater insight.
Low salt is okay. A healthy diet consists of fresh vegetables, fruits, whole grains and beans; low in saturated fats, no tobacco, no more than one drink a day. Avoid packaged foods, limit salt intake to less than 2000 mg/day or better yet less than 1500 mg. Do not rely on slogans.