BBW is a categorization tool used by men to describe women sexually, and yes it does mean fat, and yes fat is not necessarily the same as being beautiful. Go type BBW into google and what you will get is porn, porn with fat chicks. Guys who want fat chicks know this and they know to type BBW into Porn Tubes if they want to find women who are not skinny.
It took me forever to figure out what Spinner meant, and lots of women who would also say they are spinners are not they type of spinners that you guys into anorexic chicks would like. It is no different.
Women over a certain size and who do porn, are webcam girls or who are SP's know that they should classify themselves as BBW so that guys who like fat chicks can find them.