Learn@UW - When Viewing Quiz Results for One Group, "Export to CSV" Includes All Students in Course
You can view the quiz results for a particular quiz for one group of students on the "users" tabbed paged of "Grade Quiz".
However, if you export the results using "Export to CSV file", the exported file includes all students in the course who made quiz attempts instead of only students in the selected group who made quiz attempts.
This means you cannot export a large amount of quiz data one group at a time.
This is a known issue.