The article says the stretch of water is 20 to 30 m wide. The photo shows that it's more like 200 to 300 meters.
I didn't see it mentioned that foxes are an introduced species on the mainland. Humans, bats, rodents and dingos were the only placental creatures on the continent when Cook arrived.
Actually, there were two pre-human waves of rodent arrival. Millions of years before humans. All related to those in New Guinea. They have broken off into several native subspecies.
Since European contact, many more creatures have arrived and gone feral.