I assume this is due to the subtle semantic differences between "dinner" and "supper", particularly in the 1800s and early 1900s (up to about WWII). "Dinner" a

I assume this is due to the subtle semantic differences between "dinner" and "supper", particularly in the 1800s and early 1900s (up to about WWII). "Dinner" at that time referred to the mid-day meal (often the largest meal of the day: laborers needed the food to get through the rest of the day, it's hard to have a big meal without good lighting), while "supper" is the evening meal. Source/anecdata: my grandfather, who, born in 1916, referred to "dinner" as "supper" until his death in 2018.