Imagine your dog had a dog trainer and you didn’t know the dog had been trained to bite under those circumstances. You might have a case against the trainer.

you, the dog owner, would have a case against the trainer.

you, the person being bitten, would not give two craps about some story from the dog owner about how they hired a bad dog trainer who against their wishes secretly trained them to bite people.

you have been bitten. you have a case against the owner of the dog who bit you.