"An S Corp operating as a partnership would also file Form 1065."
An S corp must file Form 1120-S.
https://www.irs.gov/businesses/small-businesses-self-employed/s-corporations
To operate as a partnership and file Form 1065, the business that had made the S corporation election would have to revoke the S corporation election.
Perhaps what you have is an LLC operating as a partnership, not an S corp operating as a partnership.
