I've had dogs my entire life. I've been bitten by dogs. But I've never even heard of a dog biting off someone's hand as that poor soul was trying feed it. If you see a starving dog and want to feed it, out of an abundance of caution you put the food on the ground on walk away. By definition you don't know if a strange dog is vicious. But the point is that a happy dog normally doesn't dismember you.
There is this case which I just found, where a dog bit off five fingers off a baby:
https://winknews.com/2023/06/21/puppy-bites-baby-fingers-off-port-charlotte/
“This particular case is the first one of this nature I’ve seen in my whole career,” Brian Jones, the division manager for Charlotte County Animal Control, said. Jones has worked 25 years with Charlotte County’s Animal Control, explaining he’s never seen or heard of anything like what happened at the Port Charlotte home.
There was no indication that the baby was trying to feed the pit bull.
I won't put up other links here, but there is another case worth noting:
The parents of a 4-year-old Layton boy who was playing in their backyard when huskies bit off his hand in March are suing their neighbors, saying the dogs were known to be vicious before the attack.
What can be safely said is that vicious dogs have been known to bite the hand off a stranger, but even then the stranger wasn't trying to feed the dog. But it is also safe to say is that it's a bad idea to try to feed a dog that isn't your dog.