We are whitelisted with many email providers so that our customers' campaigns are not blocked. In setting up this arrangement, they required us to get a feedback loop in which they provided us with instant reports anytime one of our customer's list members clicks on their 'Report Spam' button. The reports you see in your account are a record of what the email provider reports to us. If a person with an email provider that we do not have a whitelist agreement with has filed a complaint to our abuse desk, it will also show up in your spam complaint report.
There are cases of people accidentally hitting the 'Report Spam' button. All we can do is report to our customers the information that these email clients provide to us. According to their computer systems, the list members you see in the spam complaint list clicked, whether intentionally or accidentally, on their 'Report Spam' button.