The American buffalo have been called Buffalo for almost 400 years... since the European settlers arrived here and saw an animal that looked like their European Buffalo.
We named cities after them, like Buffalo, NY; Buffalo WY; we had the Buffalo nickel named after them, etc., etc. They have always been called Buffalo.
To be correct, their genus & species Latin name is Bison, Bison.
So in the last 20 or so years, the politically correct biologists began calling them Bison.
To me they will always be American Buffalo, or just Buffalo.