Given his state of health, it's unlikely he was the one who put her there. It's also unlikely to have been Amanda, since it was a part of the game kept secret from her. So Jigsaw was probably lying about being the only one who knew.
She was rescued at the start of Saw V by Hoffman. Clearly he knew her location and presumably he put her there. Rescuing her made him a hero and consolidated his position generally. What more is there to explain?
