by Ken Task.
What version of Moodle?
"Course backup area" as well as some in the "User Backup Area" are kept in the 'sea' of files ... moodledata/filedir/ DB query of mdl_files for contenthash then deciphering contenthash tells you the 'path' in filedir/XX/YY/XXYYxsdflwjfqdwjflfdkjdfl ... filename contains .mbz.
To get rid of them ... assuming your autobackups are working ... cannot you delete where you see them?
There's also another area ... user private files ... to see those, login as that teacher ... then you can see/delete them.
'spirit of sharing', Ken