what is discriminatory accuracy?
In this study, "discriminatory accuracy" just refers to (sensitivity + specificity)/2. The authors calculated a sensitivity of 81.2% and a specificity of 91.9%, so their "predictive accuracy" was (0.812 + 0.919)/2 = 0.87.
For a dichotomous test, this is the area under the ROC curve (AUROC).
This is not a standard definition of discriminatory accuracy.
The question is intended to make you consider whether the authors' calculated sensitivity and specificity in this sample of 296 women represents the true sensitivity and specificity of the RST index test as applied to the the entire population of 2464 unselected women.