Should I confront my daughter about PDA?

I just got off of the phone with my sister, who my family is very close with. She says that she saw my 16 year old daughter at the mall today with a boy, and she asked me if I knew the boy she was with. (We are a pretty nosy family, I guess you could say. She umed that I already knew the kid, which I did not.) She said my daughter was kissing and cuddling with this boy. That was odd to me because I did not know that my daughter had a boyfriend, and she had actually told me that she had never kissed a boy before, when we were talking about it just a couple days ago with her mother. I am upset that she lied to me, and I want to know who the boy is, just because she is my daughter and I feel like I should know. Should I confront her about it? What should I say without ratting out my sister, because I don't think that my daughter saw her aunt there. Would it be nosy to say anything about it? I am kind of upset about her lying.