I have no idea what it is, hence the question mark. But it suggests to me that someone could report seeing a very big black cat that wasnt a house cat and it could, in fact, be true.

Just to be clear, I don't buy into all the black panther stories that I have being hearing all my life either. But, I guess it could happen with panthers if it can with other big cats. Otherwise it is kind of like saying that it is possible to have an albino deer, but not an albino buffalo.