And I'm not sure it's a mistake. If you're getting your information in a context where you know it's meant completely literally and nothing else (e.g., Omega, lawyers, Spock), then yes, it would be wrong. In normal conversation, people may (sometimes but not always; it's infuriating) use "if" to mean "if and only if." As for this particular case, somervta is probably completely right. But I don't think it's conducive to communication to accuse people of bias for following Grice's maxims.