Alcoholics who are in withdrawal sometimes hallucinate. There certainly are more causes for hallucinations than just schizophrenia.

It can be hard to know for sure if someone hallucinates. I would not assume that someone hallucinates, just because they say they do. I have actually seen people who were hallucinating, when I worked in hospitals. In one case, for instance, I saw a man talking to a person who wasn't there. He asked me why the person wasn't answering him. When I've witnessed people hallicinating, it was clear to me that they had no idea that they were having a hallucination. Afterwards, they usually had no memory of the hallucination.

When a person is hallucinating, medical professionals call their state of mind "psychotic." A psychotic state of mind is generally defined as a state causing a person to be unable to distinguish between reality and unreality. It can be temporary or chronic.