But by putting a strong password on your network, you have prevented any unauthorized hackers from getting on to attack you. Avast can’t know this, all it sees is the local machine.
Not exactly. Using a strong password on a single device doesn't protect all of the traffic going through the device. Switches/routers are just "dumb" devices that send traffic to and from a source and destination. If those devices are configured with transport controls such as port forwarding, you could have problems beyond the strong password.