I am a suthener who has moved tup north and i finaly understand this.
Dinner is traditonaly the hot/main meal of the day.
Up north the main meal was eaten at mid day as they spent a hard day doing hard work. Then they would come home to a smaller meal a exactly 5:00 and supper later.
Down south as we did less phisical work we had a light lunch at mid day then dinner in the evening with the family traditionaly later than 5:00