They were shouting it at king arthur (the taunters clearly knew who he was, he was introduced as such), I think his parents could afford the costs to get what ever shipments they wanted, be them from France... Or [shudders for comedic effect] Scottland.

You are correct in that people used what they had, and that is entierly the joke. Wine made from elderberries was much more common up north where imports were not something people had... Unless they were of nobility.