There are a few reasons you may see a surprisingly large number of opens for an email you sent.
- It has been forwarded on by the recipient to a team, so there are multiple individuals opening the email (likely multiple times each).
- The email is a part of a thread, so every time there is a response to a subsequent email, the original email is counted as 'opened'.
- It was opened by the same individuals across multiple devices (laptops, desktops, mobile devices, etc.).
Most likely, it is a combination of multiple reasons.
If you are seeing fewer opens than expected, have a look at this article.