While that is sort of true, I don't remember Clem ever making a big deal about it. Maybe I'm forgetting something, but as far as I recall, whenever you actually talk to to her face to face she just accepts and moves on. There's never any inclination that she would think it's important enough to need to tell her parents.
Plus I think Clem is smart enough to realize that kind of info would not paint him as a good guy, even though she knows he is. It doesn't make any sense to me that would be one of the first things she'd want to tell her parents.
~Mirror, mirror, on my floor, am I the prettiest at the store?
She wants to tell her parents because, well, they're her parents. Hiding things from your parents is bad, even if it's for Lee. If possible, she wants to be as truthful as possible about him.
If they asked Clem "Where did Lee come from?", she would have to outright lie to them. While she does know that it's not rationally a good idea, she "feels" it's right AKA it's ethical. Hope I explained myself well enough.
Call me Mega, Megaman, X, or any variation/combination of the previously stated names. Official Liu Kang of the PS3 Mortal Kombat board.
In Ep 2 at the motel, you see Clem talking in the walkie. I was truthful to her since Day 1. So, when you get to a free roam part to engage dialogue I asked her about the walkie. She said the walkie didnt work, I reminded her of the truth, her parents are probably dead, and she responds that she just likes to pretend to talk to them. Later on the train when she said that, she was talking about everything in general, gun, hair, and map. But I assumed she was gonna "pretend" talk like usual, but later you find out about the stranger. I dont know when the pretend stopped and he started talking to her, but thats how the stranger knows everything he does. Theres noway he started at the motel scene though, that was before the station wagon scene.
It probably happened the day after they took his food. Episode 3 took place a week after that. He probably spied on them, saw her talking on the walkie pretend and then chose to talk to her through it and she asked him about her parents when he said they were still alive.