The QoS setting of the client is the maximum QoS that it can receive. For example, if a message is published at QoS 2 and a client subscribed at QoS 0, then the message will be delivered with QoS 0. In your example, the server publishes at QoS 0 and the client set a maximum QoS of 2. Here, the message will be delivered with QoS 0, because that is the highest QoS that the server offers. See this Mosquitto documentation for an explanation of how the QoS setting works.