It was a transfer, because I hadn't named a TA when I booked on board the Fantasy in December. When I transferred it to DU last week, it was considered a transfer to a TA, but it had to be the same TA who had booked the cruise I was onboard when I rebooked. It is a transfer, because I didn't have a TA on my reservation for the first 2 months and then asked them to transfer the reservation to my TA. If I hadn't booked the original cruise with a TA, I would not have been allowed to transfer the rebooked cruise to a TA.
The transfer process involved requesting the transfer on the DU website, getting a form by email, faxing the completed form back to DU and waiting for confirmation (which I received within a couple of days).