This is just wrong

https://github.com/moodle/moodle/blob/c6211a68b4f43754a9d593d5cf3f33f42c118c21/mod/quiz/backup/moodle2/backup_quiz_stepslib.php#L51

The bit of the backup corresponds to the quiz_slots table (different name because backwards-compatibility). The columns in this table are acutally https://github.com/moodle/moodle/blob/master/mod/quiz/db/install.xml#L58

I am a bit surpirsed this does not break any automated tests!