Sumatran tiger cub born at Cairns Wildlife Safari Reserve - Cairns Photo Galleries | cairns.com.au It's a girl this time.
If it has the same parents as 'Pi' who was born last year than it is not a pure Sumatran as the male is pure but the female is a generic tiger.
Unfortunately I think you're right. With such a surplus of available sumatrans in the region, I'm surprised they didn't think to use one of them. Not to mention the age of the female.