the bear is pretending to be tough - bluffing, essentially. these tourists are not being chased. bears are generally too lazy to chase much of anything. they're just being given a spook so she can walk through with her cubs. and the cubs frankly look like they're enjoying the excitement...

these people are consequently in no danger, so long as they keep back like they're being herded to.

http://www.youtube.com/watch?v=6jQd9-aBp6E