He wasn't clairvoyant; his delusions just bore some coincidental and minor similarities to modern developments and had more to do with the pathology of schizophrenia than any insight on Dec's part. It's common for schizophrenics to experience paranoia, egomania and a sensation that they're being controlled by an outside force, and it was these experiences that shaped Dec's delusions; not clairvoyance or an extrapolation of future social and technological trends.