It's an interesting question. I don't like the word 'real' for describing hallucinations and delusions. First, they're 'real' in the sense that the people who experience them will change their behavior in response to them. Second, I believe there is meaning in these experiences (at least to the same extent as there's meaning in dreams - some dreams have meaning IMO and some seem like random nonsense ). To tell the person experiencing a delusion that it's not 'real' negates what is very likely a profound and important experience.

For example, during my son's last episode he had an elaborate delusion that he was married to three women and had seven children and each child was born with a dragon (he told me later that he somehow knew he wasn't able to care for a child, hence the dragons). To me it's a touching delusion that says a lot about his longing for connection and love and family. It was touched off when the last gf 'broke up' with him by just not responding to his texts anymore. It was just too painful to accept, so he rejected 'reality' and created a 'reality' more to his liking. She hadn't broken up with him. They were married and had children. (Then the delusion got more elaborate over time. That's how it always seems to work with my son. It's like a snow ball rolling down hill, picking up random stuff on the way.)

I prefer the term 'concensus reality.' Maybe only Atypical can see the staring guy, but that doesn't make him not real. He's just not a part of concensus reality.

The problems come when the person experiencing the delusion expects the rest of the world to accept it. My son, for example, would call the police to report non-existent crimes. Once he called them to report that his uncle had raped his wife. When you make a call like that, the police have to come out and investigate - and my son is scared of cops.