okmatewanker

In the southern US, they refer to the midday meal as dinner and the evening meal as supper.

In the rest of the US, the midday meal is lunch and the evening meal is dinner.

OP is saying that, since it's called Christmas Dinner and not Christmas Lunch, it must follow Southern tradition.

However, as a US Northerner, we've always had Christmas Dinner in the evening. So OP is celebrating differently than we do in the north.

But that's just the US debate. OP included "Tea" as the evening meal, which isn't something we do here in the US, so I suspect they're talking about a UK debate.