Come on. It seems the consensus around here is that every dog attack is never the dog's fault.
When the dog was raised under the care of a human being, it isn't the dogs fault...barring any mental issue that makes the dog aggressive. Not like, "the mother developed fear aggression so the pups were aggressive." No, I mean like the mother was a little off her rocker from birth so a few of the pups came out the same way. As in, a diagnosable mental issues. There are dogs that are aggressive without the typical warning signs and sometimes the 'expert' answer is to put it down because either a) someone royally fucked that dog up somehow while raising it or b) it was born with a mental issue. I just had the whole aggression discussion with two idiots in another threat that Knny locked thankfully, I don't care to do it again.
If a dog is aggressive, you can easily test for that when it is brought into a shelter, at least to the point of "It is 50/50, so stay away". Not to mention its overall demeanor, anxiety, confidence level, posture, energy level, reaction to strange noises, etc etc etc.
Someone screwed up. People who work in shelters LOVE dogs, and most of them are volunteers. I'd bet my life that this was a case of "Awwww you are so big and cute, I am going to come into your cage and pet you because 'Hey, if you aren't growling and snarling at me while I look at you, you aren't aggressive'". I know plenty of absolute animal fanatics, even those who heavily support PETA, who really know nothing about how to act around a dog, albeit a strange one.