Sending a copyright transfer
The key word in that statement is assumed. That means that they believe that your submission and their acceptance of your manuscript implies that you have agreed to transfer the copyright to them. They are basically saying "you don't need to send a form transferring copyright, because you did so by allowing them to publish.

If there is a reason this is not the case—for instance, all the authors are US government employees, so that the work is in the public domain—then the publisher should be alerted for guidance.