I gave a hand with this effort on Saturday. Apparently it was originally an unmarked illegal trail that was marked accidentally by some good intentioned Boy Scouts who were helping the park in an approved effort to update trail markings.
The up side to shutting this trail was that the good faith is helping the relationship with the park. After shutting the trail we also worked on opening up a small piece of trail that the park agreed to....granted not nearly as fun as the closed one. There are also discussions on some other work in the future. That's progress even if small.
I believe you are correct - it was illegal in the first place.
Thanks for the efforts to help. Much appreciated!