Such a shame. I've met more than my fair share of Boxers and they're amazingly sweet dogs.
I have a very strong feeling this was another one of those misunderstood dogs who had a behavioral problem to which the humans were oblivious. When the dog was quarantined for nipping an adult, shouldn't they have evaluated, not only the dog, but the HUMANS as well? Alas, we live in a culture of quick fixes and diagnoses, and I don't know if the shelter had the ability to point fingers at the dog's owners anyways.
Sad sad sad.