This story is consistent with a defensive attack by a black with cubs (ie similar to many/most grizzly attacks). Herrero reports at least one similar incident, also with a mother black bear and cubs. Not the most common encounter, but they do happen. And the best defense is generally to be calm or play dead (ie convince the mother that you are not a threat to the cubs).
To paraphrase the old joke: "What does a 500lb bear do...". And the answer is anything it wants. The best strategies are found by looking at the statistics--attack victims tried X response and outcomes (eg unharmed, injured, killed) occurred some percentage of the time. The best strategy is the X with the highest percentage of unharmed and minor injuries. But bears do not always act in the high percentage ways so if the standard best strategy doesn't work, the victim may have to try a different strategy.
Non-habituated blacks most commonly avoid the human (act big, make noise to chase it away), but occasionally make predatory attacks (with the intent of eating the human, fight back), and females occasionally make defensive attacks to protect cubs (be calm or play dead).
Doug
