The "password" you are currently using only gives you the ability to delete your own posts.
("If you'd like to have the option of deleting your post later, please provide a password (CASE SENSITIVE!"):)
It has nothing to do with who is permitted to post.

To use a truly password-protected message board, you first have to register. Anyone can post on this board without registering first which is why this message board is subject to so many "Bot-generated" posts made by computers.