That turns out to be just one of several possibilities, with historians having competing theories backed with evidence. The Beau Fleau naming origin has been contested. And two of the alternative theories do in fact point to Bison as the origin.
One is the native name of a chief that made his home on the Buffalo river was called a Buffalo in their native language.
The other dates back to a supposed miracle during the early French years. During one particularly harsh winter storm, with the company starving, a handful of Frenchmen said their were heading out to hunt Buffalo. They returned quickly with meat for everyone to eat, and all was well and merry! (Though they purportedly lied about the Buffalo meat, and had killed a horse and returned with horse meat).