A 'qualified teacher' is somebody who has the requirements and degrees of qualification for effective language teaching. It has everything to do with professionalism and study and nothing to do with holding a passport (the passport of a country where the target language is spoken).
Although an untrained native speaker may play a role in the language classroom as a 'teaching aid', the average speaker of any language is as unable to teach it as she/he is unable to describe and explain the working of their own digestive tract.