First off, "pit bull" owners have every right to get their dogs groomed at a grooming salon just like every other breed does. Just because they have short coats doesn't mean that all owners are capable of bathing their dogs. For instance, my mother has had numerous back surgeries & cannot bend over a tub or whatnot therefore takes their lab to have her bathed. And the lab has a short coat.
IMO it was totally the fault of Petsmart & their irresponsible employees. Rule number one when closing a kennel door is to pull on it to see if it's properly closed. Period. At the clinic, we had a case where a Lab/GSD got out of it's kennel because a tech didn't close it properly & the dog attacked 2 of our clinic cats before we could get a hold of it. We've also had an incident where a German Shorthaired Pointer was loose when we arrived at the clinic in the morning, only to see that dog had destroyed anything & everything within his reach. Again, it wasn't the dogs fault or the owner's fault, but an irresponsible assistant's fault.
Although Petsmart will likely call this a "tragic accident" on their behalf, it is an "accident" that could totally be prevented if they took an extra 10th of a second to be repsonsible & check the kennel doors.