The earlier statement was accidental. This man, the Master, Morgana has seen before -- inside the Doctor's head. He was dancing with the woman in the red dress. Thus, she has to stop looking at the Master, who, she hopes, has no idea the significance of her statement.

Wisely, Morgana does not add to her earlier faux pas, and plays it off as if she was actually talking to the Doctor. "You will just have to do without music, Doctor. If this was a proper tournament, you would have better luck."