So they found maybe a piece of an airplane, in an area near an airfield that saw extensive aerial combat in WWII. Every time Tighar finds aluminum, the skeptics say it is from a WWII airplane that crashed 150 miles away.
From Wikipedia: Today the airport is the primary air portal into Bougainville, and even 75 years after the war, wreckage from the military use of the airfield by the Japanese and Americans is easily found in the area.