In "Safe Harbor," when David is discussing his and his mother's trauma, what cryptic comment hints to the reader that he has yet to reveal some major source of trauma?

When David is talking about his and his mother's trauma, he talks about her thinking that she is carrying more trauma than he is. But, he points out, he is the one who "saw it," not his mother (129.) This hints to the reader that he has experienced something terrible that the reader does not yet know about.