Although in the US we typically use the names Bison and Buffalo interchangeably, they are indeed completely different breeds of animal. Items produced from bison vs. buffalo leather hides, however, can be quite similar. The distinctive grain of bison and buffalo hides is unique and desirable; to preserve this feature, the hides are not stretched during the tanning process. Since their hides are not stretched, bison and buffalo leather is thicker and more durable than cowhide (traditional cow leather).
Most likely, if an item is described as bison leather or buffalo leather (at least here in the US), it’s actually referring to leather from the American Bison. The American Bison is found only in North America. Early American settlers called them “buffelo” because of their similar appearance to the buffalo, and the term stuck - but it’s actually incorrect. (Regardless, most bison and buffalo leather sold in the US is indeed from the American Bison.)
It’s perfectly normal to use the terms interchangeably - but if you’re looking for leather from an actual buffalo, you’ll need to pay close attention to where the leather is sourced from. The two main buffalo species can be found in Asia (the Water Buffalo) and Africa (the Cape Buffalo). The Asian Water Buffalo can be found in both plains and marshes scattered throughout Asia, while the African Cape Buffalo roams the grasslands of southern and eastern Africa.
Appearance-wise, the grain of the Asian Water Buffalo hide is fairly similar to that of the American Bison; however, the grain of an African Cape Buffalo hide is quite distinctive from the others.