That statement about high bias and high variance is based on train set error and dev (validation) set error rate
Here is a discussion which explains a little more detail using the course material as well as other data
In some cases, when a model is created using a validation and train set dataset and then used in test dataset, the model might have given greater result on the train set with validation set (overfit) where as when the same model was tested on test set must have shows a poor performance indicating high bias on train set compared to test set.
Regards
DP