There is another, nearly identical reflection about 750 meters to the south, on the edge of a big blob of coral. I'm going to lean toward sun reflecting off of the water. I can find endless evidence of sun shining off of the surface of the water in satellite images of the south pacific. The tide also comes in and out each day.
It sounds like you are so in love with your theory that you willing to make leaps of illogic to meet your needs, which is what the conspiracy theorists (Japanese capture and others) tend to do. Fuzzy objects, shadows, bits of coral or reflections become airplanes, barges, altimeters and Japanese commandos.