The Korans were part of a fairly large pile of stuff which was taken off of prisoners over the coarse of months. Finaly the time came to clean out the ConEx all this stuff was in.
Local Nationals are used for such labor jobs, to include handling garbage.
Local Nationals disposed of all that stuff, including the Korans. It's very likely they didn't realize their holy book was among the items.
Trash is disposed of in burn pits. When the Local Nationals disposed of the ConEx of 'junk', they naturally took it all to the burn pit, because that's where they take all the trash from all over the base. Nothing unusual here.
Other Local National workers on a regular garbage rout were dumping a load when they noticed burning pages of the Koran in the burn pit where the 'junk' from that ConEx was disposed of by other Local Nationals.
Oops, **** happens.
US soldiers did not take Korans and burn them. This was an accident thru a garbage detail manned by the very people who are protesting. No one's at fault, there is no criminal intent to incite a riot, it was an accident.