CLASS-MON does not store any user data. All data is stored only in the spreadsheet, which is the property of the user who creates it, and in the form, which is also the property of the user.
All the permissions that CLAS-MON requires are exclusively to perform the functions that have been detailed (create forms, import from Classroom...). In no case is the data taken from the data sheet or the Google forms. Thus, data security is provided by Google's servers.