The text said that they begin in the age of 15 or 16, so the "duale Ausbildung" system is meant by that, because "Dualstudenten" are usually 17 or 18 when they start. The "Dualstudium" combines the practical "Ausbildung" with an applied science bachelors degree like CS, EE, mechanical engineering and so on, so it double the stress, but you'll also get a lot of work experience, a bachelors degree and an apprenticeship diploma. Also you will get paid.