Since when are Buffalo and Bison the same animal?

If they think kids say the darnedest things, then my fiance must be a kid at heart. We were at a restaurant the other night when both he and his sister ordered burgers. He got beef and she got buffalo. He then asks if buffalo is on the endangered species list. We all looked at each other and were like, he didn’t just say that did he? I of course laughed and said that I didn’t think it would be on the menu if it was an endangered species. Then he says that maybe it’s bison that’s on the list then. This kid needs to get an animal encyclopedia or something. I say to him that buffalo and bison are the same damn thing. Gosh, he makes me chuckle.