Yes, the article is wrong. A QoS 0 message is never resent by a well-behaved sender, so it could not be duplicated. It might not even leave the sender's network

Yes, the article is wrong. A QoS 0 message is never resent by a well-behaved sender, so it could not be duplicated. It might not even leave the sender's network stack if the connection was broken before the send attempt.