There are other psychotic disorders beside schizophrenia. Schizophrenia is sort of a full packet of different symptoms, and hallucinations is just one part.

Also all hallucinations are not psychotic, some are brought on by epilepsy, fevers/brain inflammation, or in rare cases people can hallucinate out of self suggestions. Finally, there is a specific kind of dementia that gives you hallucinations. Also I think some people can actually see into other dimensions.