Thanks for flagging this – this was a mistake in the website docs! The --exclusive flag is available on the textcat.manual recipe (to define whether the options should allow multiple selection) and in textcat.batch-train to configure how to update the model with the examples.
We don't currently use it in the binary textcat.teach recipe. That said, exclusive_classes is a keyword argument on the TextClassifier annotation model, so you could try to set it in the textcat.teach recipe and see what happens. I'm not sure how it interacts with the active learning – but maybe you'll see an improvement in suggestions!