A story about incest is a story about relatives going at it. A story about racism is a story about a powerful racial majority oppressing a disempowered racial minority.

Did the plot of the infamous barista story involve racial oppression? No, so I would say that it's not about racism. However, in that it demoted a character of color to a lower social status, and in that that is a trend in predominately white fandom, it can certainly be said to contain racist tropes. It may even be called a racist story if we believe it contributes to actual oppression by affirming racist prejudices and practices.

I suppose I'm using a rather narrow definition of what a story is "about." :)