Hello again!
That applies for any content that wasn’t created by you. You cannot publish a template as it is.
What you can do, is to use a template as a starting point and add your own design and features to it, remove the features you don’t need, make it unique and different from any other island made based on the same template.
If you manage to create an entertaining and immersive experience, the public will be more attracted to your island! Even if it is based on a premade template.
I hope I have been of help!