Think what you say here is basically correct. There are many sites that claim a 100% cure for diabetes using Cider or Apple vinegar. The name Dr Kenneth Pullman comes to mind. He is neither a Dr. or associated with Stanford University, and he is out to take your money. If you google quackwatch cider diabetes, you will find others.
Having said that, Jason Fung does recommend the use of cider. His explanation is basic GI lowering, and is written up as:
https://intensivedietarymanagement.com/the-benefits-of-vinegar-hormonal-obesity-xxviii/
Since Jason is not advocating a cure, and not charging directly for his 'secrets', then I have more confidence in his appraisal. Personally, i tried it once, and only once. Not for me.