Being 'out the front on a chain' and being used as a deterrent, he would be displaying the normal warning signs to the intruder, any intruder game enough to get near enough to be within striking distance is very determined .. either that or the dog came out of nowhere and took the intruder by surprise, Dogs are not destroyed for a single bite, it would have been investigated and deemed to be "a danger"
as far as a my comment regarding animal cruelty being a reportable offence, i was incorrect... i apologise to the mods and 'whiteyluvsrum' it would appear that the orgaisation responsible is somewhat of a toothless tiger,
to clarify the details, I found this on their website,
"Unfortunately, hunting of pigs with dogs is still a legal activity in some parts of Australia, including Queensland and New South Wales. This allows dogs to be used to flush out or locate feral pigs but they are not permitted to bring them down, however there is no evidence that this distinction is being enforced in either State."