There, he cared for Allied prisoners of war who were forced to work in horrific conditions. To the Japanese ear 'MacCarthy' and 'MacArthur' were indistinguishable. The Japanese assumed that MacCarthy must be a close blood relative of the American commander.
He tended to Allied POWs held under horrific working conditions.  The Japanese perceived "MacCarthy" and "MacArthur" as identical, assuming he was related to the American commander.