They probably don't know the difference. They don't specialize in them and just sell large lots of cb and fh and many times mislabel them which just adds to the confusion that new keepers have about the 3 species.
The snake pictured is a python brongersmai. Python curtus curtus is an outdated term that refers to the black blood now known as python curtus. Post pictures of your snake when you get it and we'll tell you what it is.