We can't really know what the therapist intended, of course, and it would be hard to make any kind of inference without a lot more information.

So far, we've identified three possibilities:
-He was trying to reflect.
-He was making a joke.
-He's a jerk and insulted her.

Another possibility comes to mind: paradox. He hears the client putting herself down and criticizing herself for being foolish. He calls her a cold turd and hopes that this will rile up her defenses. She'll see that label as "going too far". She'll point out that she was just a kid, and that lots of teens have the same delusions she had. She might even mention a positive thing or two about herself. It's an attempt to get her looking at herself in a more positive and balanced way.

I used to look at techniques like that as cruel and tricky, and I'm still not comfortable with the deceptive aspect of it, but I've seen it work wonders. If the therapist had said, "C'mon, aren't you being too hard on yourself? Aren't all teens like that?" it might come off as dismissive and minimizing your friend's pain. Paradox helps her come to these conclusions herself and that's usually more meaningful.

Of course, paradox can fail spectacularly, too! Maybe that's what happened here. Or maybe he was just trying to reflect, or tell a dumb joke, or maybe he's just a jerk. I think you're on the right track by asking your friend what she thought about it. Her opinion is the only one that counts ultimately.