"fried chicken sandwich" outside America vs "chicken burger" seems to depend on whether you use a burger bun or not, at least that's my observation. The secondary observation is that for dietary reasons a lot of places don't primarily think of burgers as exclusively beef or pork so the swap/substitution is already well underway for what makes a burger patty/filling.
(ETA: so by the time our English settled on understanding a burger is a sandwich using burger buns, then just about anything in the middle can sub for a meat patty)
In the United States, the sandwich usually consists of a chicken filet or patty, toppings and bread. The chicken meat can be deep fried, grilled, roasted or boiled, served hot or cold, and white or dark meat chicken can be used.
and @cendawanita@cendawanita@monyet.cc already explained it you by way of a screenshot from another source from Wikipedia.
it's quite funny because you defeated yourself with your own logic, and when pointed to various sources you rather ignore them but choose to downvote every single comment that do not agree with you. It still won't change a damn thing that it's called a Chicken Burger outside of NA