I have a little trouble with the idea that someone would ditch with the gear down. I suppose they could have landed on a beach and had the plane washed out to sea later by a storm.
The skeletal remains and evidence of a camp on Nikumaroro seem to have been pretty well investigated by the British colonial authorities. They attributed them to a middle-aged, probably native, man who had died at least twenty years before the remains were found in 1940.
Did the landing gear retract on that plane? I don’t know. It just doesn’t look like retractable gears in the picture.
And speaking of pictures. I also want to see the picture they are talking about.