There is one possibility explaining this. Just speculating here.
Paul Jaquays wrote an adventure called The Enchanted Wood for the Draqon Quest game, which I think TSR at the time held the rights to, and many of the elements from that module got included in FR5. It might be that Aurilsbaarg was one of those elements and one that later Realms writers found to not fit the Realms.
This might be a good question for one of the Authors of the North box.