I wasn't judging the Perth National last year which was the year that it won that. (I overheard, or it was meant to be so) that the "national body" wasn't too happy about it, whatever that meant.
I've viewed the image in quite good detail (online) and can say that it all looks legit. The light angle is right each of the birds so they were shot at the same time and one can't tell if they weren't. From memory, there is some slight haloing about the Spoonbill but that is likely from the entrants PS/PP ability and having to push some light in the right areas to pull it off - the dark areas would have been a bit too dark to appreciate the image fully. I recall the rules indicate something like "any post processing must not be obvious or alter the image content" or something along those lines.
The photog does produce some excellent work and it's a pity he has chosen to retire. Having said that, he has reached a pinnacle of achievement and that's what I told him.
What is your concern with the winning image, Feg?