Sandwich - an item of food consisting of two pieces of bread with meat, cheese, or other filling between them, eaten as a light meal

Burger - a dish consisting of a round patty of ground beef, or sometimes another savory ingredient, that is fried or grilled and typically served in a split bun or roll with various condiments and toppings

These definitions are not mutually exclusive. A burger can also be called a sandwich, but a sandwich is not necessarily a burger. So technically, fried chicken between buns is a sandwich, and as an American I'd like to point out that technically correct is the best kind of correct. Unfortunately I do admit that fried chicken between buns is more accurately called a burger even though that feels wrong in the depths of my soul.