Understanding ConfusionMatrix for Google Prediction API
As explained in the documentation:


  This shows an estimate for how this model will do in predictions. This is first indexed by the true class label. For each true class label, this provides a pair {predicted_label, count}, where count is the estimated number of times the model will predict the predicted label given the true label.


If you are not sure what a confusion matrix, see Wikipedia, where the "actual class" refers to the same thing as the "true class" in the Google documentation.