This is expected behaviour. Whenever you create file/folder using the user who is a member of Domain Admins group the owner for the file/folder will be domain Admins. Now, as domain admins is a part of builtin\administrator on storage, hence, we are mapping it to builtin\administrators.
Can be verified using below command:
::>cifs users-and-groups local-group show-members -vserver <vserver-name> -group-name BUILTIN\Administrators
If you would like to create a file/folder with owner as creator, then make sure that user is NOT a member of Domain Admin groups.
FYI: Member of Domain Admin groups can take/change ownership of any file/folder.
This is Microsoft client behaviour.
you can check refer below links:
https://blogs.technet.microsoft.com/sfu/2010/05/26/how-to-change-the-default-ownership-of-a-newly-created-file-on-windows/
https://support.microsoft.com/en-us/help/947721/a-group-policy-setting-is-not-available-in-the-security-policy-setting