A dog is an animal. It has no moral responsibility. If a dog does something wrong the fault lies with the person in charge who failed to control it. A professional dog walker should be aware of traffic and anticipate how the dog might react.
"Might" react. If it reacts in the total opposite way then what? Constrain lead to 20cm, full muzzle, sedate the dog incase it's brute power is too much in a unexpected moment of madness.
That's a weird way of spelling "Use a reasonable leash length for your distance from traffic."