I am so sorry you had this experience. I feel you. If I was very nervous about my stuttering for a particular job interview, and I feel like it might be a car crash then I would start with telling them I have a speech disorder and bare in mind my stutter doesn’t represent my confidence or my knowledge in any way. it’s very direct and it might even help your nerves puttig that out there. Also you cant know for sure thats why they didnt choose you. I think we as stutterers tend to think we sound much worse in our head than we really do.