In what particular ways do you think that David felt he was strange and wrong?

I'm not sure what you mean about how he was strange. David has never been outside of the camp, his experiences are like nothing he's ever encountered before. David worries about the way he was perceived by Giovanni and Elsa, never considering that the things he'd heard were one-sided.... the way he perceived them.

In addition, David embraces his spirituality, only to become hopeless and despairing. He uses his talents and endearing smile to get by, and yet, the things he cannot have rocked him to the core.

In context, the strangeness you allude to might mean David's eyes, which are described as strange and beautiful.... a window into his experiences, somewhat haunting if we judge them by the way they appear to the American couple, and so like Edith's, whose eyes to him are what his own are to the people who see them.

I thinnk he was strange because he was different form other kids like maria and her siblings.