In WP Viral Quiz v3.2 and prior, user data were saved even if you unchecked this setting :
It was a bug, and I'm sorry for that! It's fixed since v4.01. You can download this new version on CodeCanyon (just remove the plugin from your website (don't worry, it won't delete your quizzes) then install this new version).
You can also use the Wordpress auto update system, once you got a new notification.
How to configure v4.01?
Using v4.01, if you unchecked the box "save answers", it won't save any answer.
On the other hand, if you ask people to give you an email at the end, you have a new feature to enable local save (default is : enabled). You can choose to save form data or not localy.
Even if you sync user data with a third-party service (Mailchimp, Aweber, ...), it could be a good idea to keep a local backup of user data.