In most Moodle courses, quizzes are open book affairs. This is because when the student is taking an online course, there is nothing to prevent the student from looking things up. If you want to prevent this, you can do so with some manual intervention.

The easiest way to prevent a quiz from becoming open book is to put that quiz into a separate course topic, by itself. Then, hide all the other course topics. This can be done by clicking on each topic. This prevents students from seeing any of the course material while they take the quiz. Administer the quiz and redisplay the topics afterward.