In the South East, they bring you sweetened (usually far too sweetened for my tastes) iced tea. This is amazingly universal.
I live in NC and have been probing the border for years.
For “nicer” restaurants, the universal sweet tea boundary seems to be precisely at the NC/VA border.
I’m in South East VA and your border is wrong. It extends mostly up to NOVA, but even in NOVA sweet tea isn’t that uncommon.
As a long time NoVA native I agree sweet tea isn’t uncommon but also not assumed. I think you’d get the same puzzled reaction if you ordered “tea” as if you ordered “soda”.