The page that you referenced is for the Regression Learner app. If you look at the doc pages for Classification Learner, or use the Classification Learner app, you will see the classifier accuracy:
Regression models are predicting a continuous variable, so the regression error can be summarized through quantities like the Root Mean Square Error (RMSE).
Classification models are predicting a discrete class output, so the classifer accuracy can be summarized with a percentage accuracy rate.
