I'm afraid there is no clear-cut difference between the two. First, because everybody uses a different terminology (there is no "standard" definition for these terms). Secondly, because IMO, both terms refer to the same concept (using models as part of the process of writing the tests for your system) and only differ regarding the importance of the role of models in the testing process.
To me, model-driven implies a stronger role of the models (i.e. models are used to derive the tests) than model-based (where models are used but maybe as an additional input in the test generation process).
At least, this is how I explain other "model-based" vs "model-driven" concepts as I tried to explain in more detail here: http://modeling-languages.com/clarifying-concepts-mbe-vs-mde-vs-mdd-vs-mda/