Paul continued that it was SOP for returning planes to dump their remaining bombs in the sea before landing, and it was a direct hit on the plane carrying Glenn Miller.
I saw a show on this recently and as you mentioned, this seems the most likely explanation.
Evidently the RAF was on mission, but the wheather was bad and too much cloud cover, so they had to dumb the bombs. Unfortunately the dump spot was on the flight path of Miller's plane. One of the pilots saw a plane down there, and it was the same type as Miller's.
fwiw