As the bears in Jasper National Park, Canada, are not hunted, they have developed a population of "problem bears" which are not afraid of humans.
From not being afraid of humans, it is only one step to testing to see if those human bags of meat make suitable prey.
Not many black bears attack humans; but some do. It almost always comes from a population of bears that do not fear humans.
Some are wilderness bears which never saw a human; some are bears which have become habituated to humans.
Labrador has aggressive black bears too as does some island. Likely due to not being hunted much or at all, and becoming used to folks like you mentioned.
Bears will also get aggressive when food is scarce and they are starving, or if they are old and can’t hunt like,they used to, or are sick. Most bears are cautious, but in those 4 cases they lose their sense of caution, and become aggressive out of necessity, but it usually goes agaisnt their nature to do so