Correct, the old thread has been locked in order to start a new non self-moderated thread following the advice of the community.
Maybe you did not know.
You don't have to create a new thread to remove a self-moderation of your old thread. You can keep the old thread but moving it to Meta. In Meta board, threads are not allowed to be self-moderated and your thread will no longer be self-moderated after moving.
After that, you can move it back to Gambling board and it will still be not self-moderated.