You may also consider adding the "Not clicked link in Email" filter. While the email performance reports have logic built into them (they will count an open if someone clicks an email), the activity log does not. So, if someone had images turned off, but clicked a link in the email, they would still show up on your list.
Also, now that Mail Privacy Protection is live that these lists may now leave off people who had the open triggered by Apple Mail, but they didn't actually open the email. Just something to keep in mind here.