Perhaps most importantly my friend is not the direct slave owner, if that is indeed the relationship. It's my friend's dad, a guy I've barely even met. Perhaps if he was around, and caning her as I walked into the kitchen, I would have said something, who knows? But I was receiving his hospitality through a third party, and I am a foreigner to their country and customs.
Did you ever read the article and wonder why Billy or his family didn't do anything? They probably felt it was so alien they didn't know what to do.
You also gotta ask yourself, if you owned a slave, why you would allow that slave to be the only attendant when a western family comes through town?