It took me all of 5 mins research to discover killing a bear with a knife is not only possible its been a human rite of passage in many cultures in Europe though history and survival of said rite the norm, with some Eastern Russian tribes still practicing it.
It basicly boiled down to boy sent out alone with knife.. boy had to bring back bear pelt etc.
Lets do this from the bear perspective.
Bear 1 Hey fellow bears, im looking to kill and eat a human, I know not to go after them if they have those long stick things that go boom.. but what about those silvery shiney retractable claw thing.. its not very long my claws are longer... and I have 10 of them.
Bear 2 hey yeah sure.. go right ahead you can run them down as they are slow as anything then just eat them they have very weak bones and are easy to kill...
bear 3 Easy to kill? I had a buddy who tried that, the human despite having a crushed wrist broken leg and bleeding everywhere wouldnt stop stabbing with that little claw.. it may not look like like much but he died before the human did.. i got to eat them both but so

.
bear 4 LOLZ funny shhiitzzz thinking you can kill and eat a humanzzzz morons ask this every month and its always a grizzly you know how they are.
Bear 5 Whoo page 18 WHOOOOOOOOOOOOOOOOOOOOOOOOO!
Bear 6 Cant kill humans? I got a buddy that goes out city every week and bags 10 of them during hunting season without fail till they got protected and such. True story bro....
Bear 7 I just want to say RAAAAAAAWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR!