If he lies about that, that's another level he would have to fix before he can move forward. It still outs him and sets him back.
And even if that were true, he STILL needs to be at peace/resolved with his family past, and all the other friends he projected issues onto.
All the past relations would have to be fixed to have normal relations in the future "without" projected garbage.
So you can use this to screen people out. The stable people have nothing to hide about their families and pasts.