I'm sorry, but that's totally wrong. We had a very similar experience.
We adopted a stray dog when our son was 3. Despite my best intentions, the day came when I let my guard down and left them alone. I heard a dog snap and son cry, he in with a red mark and small broken area on his cheek. Dog had bitten him. I gave him a stern talking to about not upsetting the dig and was more careful from then.
A few weeks later a friend was visiting, I left her alone with dog while I went to loo, dog attacked friend, biting her across the bridge of the nose, without any warning in a completely unprovoked attack. Friend had to have hospital treatment.
Very sadly, when I asked the rescue centre to regime her they wouldn't consider it. She was considered to be a dangerous dog because she'd gone for the face, and the attack was unprovoked and without warning. She was put to sleep and we were absolutely heartbroken.