You may see sources you do not recognize in the ‘ DMARC compliant – DKIM aligned’ section.
This may occur if you send DKIM signed email to these sources and the recipient has configured a forward.
This would mean the original receiving server of the message will forward the message to the new destination as specified by your recipient.
This message would have a failing SPF in most cases. This is quite logical as you have not specified this forwarder in your SPF records.
However, DKIM is designed to survive forwarding in this situation providing the forwarder does not change the contents or headers of this email.
In this situation the DKIM signature can be correctly verified by the new destination and the mail is marked DMARC compliant with a passing DKIM signature!
If this new destination sends DMARC reports you will see this process in the overviews in the defined section.