Recognisable propery

If you are new to stock, you should consider these resources: https://helpx.adobe.com/stock/contributor/tutorials.html
Please read the contributor user manual for more information on Adobe stock contributions: https://helpx.adobe.com/stock/contributor/user-guide.html
See here for rejection reasons: https://helpx.adobe.com/stock/contributor/help/reasons-for-content-rejection.html
and especially quality and technical issues: https://helpx.adobe.com/stock/contributor/help/quality-and-technical-issues.html

You do not need to assume why it was refused. The reason was given. If a release is needed, the image usually lands in the Reminder tab. If it was refused, it lands in the Not Accepted tab where the reason is shown. 

Because this artwork is permanetly mounted, it falls under the 120 yr rule. This may vary according to region. This is still no protection for you. In some countries, the photo must have been made from the sidewalk or street. Not in a park. 

If it is not permanetly mounted, you always need a release. As @Test Screen Name said, the owner is the artist/designer.

By the way, if you did want to get a release, don't talk to the council - they don't own the copyright. Owning the land where something is doesn't give you copyright. Paying for the thing doesn't give you copyright (usually, though the contract to make it could assign it to someone else). The copyright rests with the creator. The internet is, as usual, vague about who that is. Some say the big fish was made in 1967 by Duralite Company in Melbourne, and paid for by Tocumwal Chamber of Commerce. Some say it was made for the movie Eight Ball in 1992. No doubt there are other fishy stories. Basically, public art is rarely a suitable subject for stock, no matter what the local council thinks.

If it's less than 120 years old, it needs a release. That's Adobe's rule. Clearly, as a movie prop, it isn't that old. If the council won't give a release, the concept of "public asset" is not defined in law or by Adobe Sstock.