According to the Federal Government web site on Australian colloquialism, to act like a stunned mullet is described as being "Dazed and confused, someone who will wander 'like a stunned mullet'; in a furious rage, they will be 'mad as a cut snake' and in a state of undeniable anger".
The change of mind by JB HiFi has not only stunned Sony, but the whole CE industry after Scott Browning the Marketing Director decided earlier this year to only support Blu-ray. At the time he was quoted as saying "Consumers don't give a rat's arse about products. They are more about buying an experience and Blu-ray delivers that," he said.
Sony at the time fell at Browning's feet for the gushing support with just about everyone in Sony using JB HiFi's decision as a key marketing tool in their battle against the HD DVD format. Today Sony executives were very quiet.