I agree with you completely. It was likely he was released under an honorable or general discharge, and it was the actual reason that is being withheld by Kerry.
There is something strange with regard to his discharge.
Something does not add up.
When he came back from Vietnam he could not have been totally discharge from the Navy.
I don't think a discharge does require a court martial. A court martial must be requested by the person accused.
He could have opted for NJP. Which means the commanding officers hands down the punishment.
My guess is if he did recieve a dishonorable discharge, it was because he violated the terms of his inactive reserve status, which was a result of his leaving Vietnam.
I doubt at the time, that the government would have pursued him given the fact that he was looking for attention.
They handed down an NJP dishonarble discharge for behavior unbecoming of an Naval officer.
I went and looked at an old copy of MILPERSMAN And found something I had not been aware of. In some cases an officer is allowed a "resignation for the good of the service to escape a general court-martial." What we would need to see now is Kerry's resignation letter which would state that reason per the manual and would be in his records. As far as I know, every officer, active and reserve, who leaves the service without retiring or being forced out has to submit a resignation letter.