They were based on a barge right among the other fireworks barges in the harbour and yes it was pure luck that they didn't get hit by any of the fireworks but as someone has already said it was a cool shot and they decided it was definitely worth it.
They were in a cordoned off area over water so if it had been hit there was little to no risk of injury if it fell and for the cost of the whole NYE spectacle in Sydney the cost of a drone is nothing.
There is the risk assessment Keg! It was a cool shot and they ( I assume the drone operator and the fireworks people)decided it was worth it. As you are in the know Trimset could you also enlighten the aviation community if they got the required approvals from CASA? FYI, approvals from NSW OHS departments don't count when it comes to operating in Commonwealth airspace.