If you marked your quiz "private" it would not show in google. Private quizzes are only visible to those whom you share the URL of the quiz with.
If the quiz was first public and then marked as private, it's possible that Google indexed it earlier. We add the noindex and nofollow directive for Google (and other search engines) on private quizzes so next time it refreshes, it should remove the quiz from search (a process that can take a few days or be instantly - just depends on Google). If you need it removed immediately you can :
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