Apex predators are not naturally scared of humans. A Canadian researcher a few years back found that Black bears kill more humans than other bears. The attacks were typically by male bears treating humans as food. This story fits that profile.
The number of attacks are relatively few, but they have become more common in recent years.
The researcher you are referring to is probably Stephen Herrero. He speculated that black bear attacks were uncommon because aggressive black bears were killed off during bear hunting season, so that the genetic pool of black bears consisted of those who were more cautious.