What isn’t in the text is Obama’s correction of (according to you) the falsity of Auma’s statement.
Obama wrote, having his half-sister state, that only the children of Obama Sr-Ruth have an uncontested claim.
You are reading into the text what isn’t there, you are reading that Obama states his claim was uncontested.
Obama recounting Auma's words about her mother doesn't magically transform them into words about Obama and his mother. But that's the sleight of hand you're trying to pull with the out of context quote and reference to the WH posting.