because the "relaxed stride" (the appearance) contradicts the "exhaustion" (the reality).
because it describes a cause-and-effect relationship rather than a contradiction of appearance. hiding her actual fear).
Test your understanding of "belie" with the following questions. hiding her actual fear).
"His youthful face belied his eighty years." (He looked young, which contradicted the fact that he was old). hiding her actual fear).
"She spoke with a calm voice that belied her inner panic." (Her voice sounded steady, hiding her actual fear).