Indeed. This happens when the form is configured to collect "verified" emails. A form can use a custom field (doesn't require login), user input managed by Goo

Indeed. This happens when the form is configured to collect "verified" emails. A form can use a custom field (doesn't require login), user input managed by Google Forms (named "Email", doesn't require login), or the google email of the user ("verified" email, requires login). This add-on supports every one of these options.