alt Hacker News> What part of the world, and how recently? Sure a burger is a sandwich, likely being a spin off of Hamburg steak.
The 95.8% of the world population that isn't in the US. This is simple to deduce because everywhere else calls "a piece of fried chicken in a burger bun" a "chicken _burger_". Only the US calls it a "chicken sandwich". Some of Canada might now use the latter through US influence - any Canadians here?
KFC is a representative example, they call them "KFC chicken sandwich" only in the US, "burgers" effectively everywhere else.
I suspect Commonwealth or Asia. Is your definition of sandwich cold things between sliced bread and burger hot things in a bun?
A piece of hot chicken between bread in Italy would likely be a panino, france a sandwich, spain a bocadillo, Portugal sandes, Japan a sando, mexico a torta, Argentina a sanguche.
I think you overestimate how many people use burger for things that don't refer to the American concept. A lot of cultures have hot sandwiches and thus (ham)burger is often distinctly the American concept of a ground beef patty. Where this breaks down outside of the Commonwealth is often from cultures without things in bread that got exposed to the generic burger via fast food chain terminology. Not surprising there.