It looks pretty obvious to me that the Captain intended a visual approach to the runway, and so descended to a circuit altitude of 1500' AGL (1600) - to then fly level and pick up the final approach to the runway. I don't think it occurred to him at the time that day & night are different in terms of respecting LSALTs when visual.
Dont forget he had been cleared to 3000' and had never been given clearance to descend.