I would be very surprised if the TIGHAR image represents anything other than a seabed anomaly. It is a very coarse pixellated image. Compare it with the stunning Dornier image that was published more or less at the same time. This was produced using multibeam technology, it is expensive but the results leave little doubt as to what is lying on the seabed.
As mentioned above TIGHAR depend on voluntary funds so every now and then they have to stir their donors up.