For me, the angle is: This cannot be allowed to happen.
Whether it's the owner's fault or the dog's, and whether the dog "normally" wouldn't do it, is not that relevant. I don't care if it bit because of uncontrolled aggression, I care that it bit.
If dogs can get away with biting a stranger, then more stangers will be bitten.
I'd be OK with some form of punishment for the owner along with/instead of for the dog, but it needs to be very strongly discouraged/punished. ...