Maybe it is sexist, but in isolation it's just not particularly remarkable or actionable.

  sexism - noun - (2) behavior, conditions, or attitudes that foster
                      stereotypes of social roles based on sex

The theory being, you're trying to impress your superiors, so your sexist response is to tell the woman to smile, and the man to look busy? However, asking your subordinates to be gracious to the boss is pretty typical.