Maybe he just wishes they'd been there to play with him and he was stating what he'd been wishing to his friend who didn't know it wasn't true, so couldn't deny him the fulfillment of that wish.
I wouldn't worry too much about it. I went out with a guy once who'd created this elaborate family - a sister who worked in advertising for McDonald's - a brother who...did something extraordinary - I can't remember what. We went to college together four hours from his hometown, so I had no way of checking anything out. I just took him at his word.
So anyway - he was taking me to meet his 'mother' and we pulled up in front of this highrise apartment building that was supportive housing for elderly people and I'm like, 'Okay - why are we stopping here?' and I'm thinking, maybe I'm meeting his grandmother first or something.
He told me, 'This is where my foster mother lives. I don't have a family. This woman is named Margaret - she took me in when she was sixty and I was seven- she's the only mother I've ever had.'
I said, 'What about your sister - did she live with you and Margaret too?'
I'm still thinking there really IS a sister. There wasn't. He admitted all of it was just what he'd wanted to have had and since I was always talking about my family and brothers and sisters - he made some up.
It sounds weird - but it wasn't. He turned out to be totally normal (just sad about not having a family).
I would talk to Mo about how important it is to tell the truth in general though.