Does this info I found on Facebook legitimately matter?

[Kelly Bellini]

I'm in the process of finding new tenants for one of our houses, and I've pretty much got it narrowed down to this single mom and her 3 kids.  But, there's just one thing bothering me, and I wanted to reach out to you guys to see if this is ACTUALLY a problem, and if I need to do anything about it.  When she came to see the house, she brought her "brother" with her, at least that's who they said he was.  He had a child, and she had her 3 children.  No problem at all.  I liked them all.  But then, I looked her up on Facebook, as I do with all potential applicants, and it actually said that she was "in a relationship" with him.  And he's not her brother.  I know this is her personal business, but I don't feel good about starting things off with what seems to be a lie.  Is there some reason to even lie about this, that I'm not thinking of?  I'm just confused, and I hate any red flags (obviously).  Should I ask her?  Or is that overstepping?  Was I even allowed to look on FB? Should I just let it go, and continue on with her credit/background check?  It seems that the only potential problem is if he moves in, and he's not on the lease, and I didn't credit check him.  But, why the lie???  Any thoughts you have are MUCH appreciated.  Thanks!!