The main thing I get from that article is that they were captive animals, in a rescue centre. Some of the worst outbreaks here have been in similar circumstances, because well-meaning people take sick wild birds they stumble across there, and thereby introduce the disease that made the bird sick; the biosecurity at the centre is usually not good enough (especially before it's known that AI is about) to stop the spread between cages, and the other animals at the rescue centre are captive so can't avoid exposure. Spread among wild birds is quite different.