When we send an Advanced Mass Email, we can use the Delivery Report to generate statistics about the email. The Tracked Opens Report, a component of the Delivery Report, tells us how many times recipients opened the email.
This multiple opens count, especially within a few minutes of one another (View Details under the Tracked Opens heading) is due to the recipient's email provider (Outlook and Apple Mail) have a preview pane as part of the inbox view. If the recipient scrolls over the email in the inbox and not truly even open it, this can trigger an open notification to the reporting. Unfortunately, this is unpreventable and cannot be distinguished from a true open.