When the guest login with the App via Facebook or links account with Facebook, it is expected behavior that the user will receive the email from Facebook for security reasons.
No information is posted on the guests Facebook account. The notification sent from Facebook that you have logged in to the App and your few personal details like Name, Email, Profile Picture are shared and saved in their account.
If further assistance is required, submit a ticket to Punchh Support. (For help submitting a ticket, click here)