If your campaign report shows that a recipient has opened (or clicked) your email an unusually large number of times, here are some possible explanations to keep in mind. It may also help to review how email tracking works.
If your recipient forwarded your email to other people, all of their opens and clicks are reported under the original recipient's name. Note that this only applies if they use the "Forward" button in their email client. If your email included a "Forward to a Friend" link, then any emails that resulted from clicking that link are not included in the campaign report.
Role or Group Email Addresses
Sometimes one mailbox is monitored by multiple people or is automatically forwarded to several people. For example, an email address like "firstname.lastname@example.org" is probably distributed to more than just one person (or maybe even a whole company). Even though different people are opening the email, all of their activity is reported under the original recipient email address.
If you copy content from an email in your inbox that was sent by Direct Mail, and then paste it back into a new message in Direct Mail to send again, then it's possible you could end up accidentally including tracking links from your old email. That means that each time the recipient opened your new message, it would record an open for the old message and the new message. In most cases, Direct Mail will warn you if it detects that you are pasting tracking links and will automatically remove the link for you.
Highly Engaged Subscriber
It is possible that all of the opens really did come from the same person. Perhaps your email contained content that the recipient needed to refer to frequently, or perhaps it was the most recent message in their inbox and was displayed by default each time they opened their email app.