so what makes an object that isnt flying, a ufo?
They're assuming, that from the extrapolated shape, that it was designed to fly.
But hey, I say what the forget do we know? For all we know it could be just some rand metal structure that aliens planted here and are now just sitting back and watching us squirm.
Or you know... it could just be an anomaly where part of the seabed is denser than the rest.
But hey... I'm just speculating.