This is a really weird story.
Properly trained sniffer dogs get happy and excited when they detect their target scent; they don't get aggressive, angry, or hostile.
Likewise, a properly trained handler never allows his animal to have more than a few feet of lead in a crowded area, and can usually pull the animal back if it gets aggressive.
It's rare for any animal to attack someone completely unprovoked, but almost unheard of for a well-trained sniffer dog to do so.
My suspicion is that the woman who was bitten somehow provoked the animal, either with her behavior, or perhaps by scent, without being aware of it. But either way, I think the handler also has to be held to account, because he wasn't able to read his animal's emotional state well enough to anticipate and head off the attack.
No matter what actually happened, I seriously doubt that the animal was at fault.