The 'clear' images are not side scan images, they are from an ROV (remote operated vehicle). You can clearly see the bright light from the ROV and the black and white camera.
If you look at the BEA website you will see the side scan image at the bottom (the dark image). You will see reference to 'AUV' in the title box, this is an 'Autonomous Underwater Vehicle'. A 'side scan' is normally incorporated into a 'towed fish', and the deeper the water the longer the umbilical and the difficulty in controlling the fish, and knowing the exact location of the fish. The 'AUV' is the latest and greatest, an 'untethered vehicle', think of it as an underwater 'tomahawk missile' with a side scan fitted, you programme it where you want it to go, and off it goes and then pops up to the surface when it is finished.
So the Side Scan gives you an acoustic return, and they can be hard to interpret. The ROV gives you a real image, and is much clearer.
So I presume they mapped the seabed with the AUV, then pin pointed the location and then used the ROV to take the still images.