Dear Soona Hong,
Thank you very much for the questions, They are important points to consider the 6th definition.
(1) About contradiction:
Contradiction is a pair of propositions, one affirmative and the other negative, as the Sophist defines and Aristotle follows in the Interpretation. Plato does not consider "category mistakes" (as Gilbert Ryle clarifies), so the examples you present should be interpreted as: "Soona is an open book" (False) / "Soona is not an open book" (True), becaus all the category mistakes are considered (if not nonsense, or meaningless utterance) false.
(2) About purification
You are right in that purification through refutation does not necessarily bring about the pupils' benefits, since they may not be happy to admit their own ignorance. Just as Socrates was hated by his fellow citizens, the purifier of the soul may not be able to change their mind. In contrast, the sophist (without using apparent refutation) may make his pupils aware of their ignorance by chance. But as far as such sophistic purification is apparent, his purification of the soul may remain apparent. The pupils may well be mistaken in understanding their own cognitive state. So although not all purifiers can successfully cure their patients, no sophist can properly cure them.
These are my tentative answers. Thank you once again.