Reading that interview leads me to assume that it must've been emotional labor for Hochschild to keep her cool at how badly people can misinterpret it.

There's physical, mental and emotional labor. The first is pretty self-explanatory, the second involves thinking and the third involves keeping your emotions in check in order to complete a task.

Whenever you have to put up a fake smile, that's emotional labor. Whenever you have to be tough, but don't want to, that too is emotional labor. If your emotional stability (or lack of) aligns with the task, it isn't. So if you're a flight attendant and smile without forcing it (thus it isn't a fake smile to begin with), there's no emotional labor involved. If you're a drill sergeant and naturally grumpy and condescending, there isn't any either.

EDIT: In the cases above, when I meant that there's no emotional labor involved, I meant that there's no effort involved. The value of the labor is still derived from the emotions nonetheless.