Yes they may "Not say the truth" so this can be equal to a lie, but not for them.
That's what my mom did, and taught me (and I assume my brothers) to do, to conceal from my non-believing father that we were going door-to-door. He didn't approve of her doing it and he had flat-out forbidden her to take us kids. To defy his "headship" would have been a sin, but to deceive him was just fine.