I don't think this can be a complete coincidence, but without further evidence than this one website I don't know if the story about the waitress is true, or if it's the French version of an "urban legend" made up to account for
Fanny being associated with "buttocks" in the context of this game. You will note that the story is supposedly from World War I, when is the time when English soldiers who would already have been using "fanny" in its vulgar sense would have been in
France. The usual explanation for how "fanny" came to have that sense in England is that it has something to do with the erotic novel
Fanny Hill, which was first published in 1749.
http://en.wikipedia.org/wiki/Fanny_Hill