CJD is extremely difficult to diagnose ante-mortem- but it seems that he exhibited plenty of neurological symptoms, and should have had a competent Neurologist examine him early on in this ordeal. The diagnostic possibilities are many, but it should have been apparent that there was organic brain disease.
And it is not as though no-one knows about degenerative brain disease in young people- I would be surprised if there were a physician (or a Special Forces medic) who does not know of the outbreak of "new variant" CJD in Great Britain.
Addendum- As much as I hate to second-guess others, it does seem to me that a Psychiatrist (who, after all, has a medical degree) should have been able to pick up the difference between malingering and an organic brain syndrome. That is upposed to be a large part of what they do.