Because it is fake.
For one, the bear sounds are ridiculously out of place. They don't blend into the auditory enviornment of the video. They were just copied and pasted on top of the already compressed audio track.
Secondly, the bear has a perfectly uniform shadow. How could that be? Especially given the lack of direct light due to the clouds.
Lastly, when the bear goes behind her, there are artifacts from what appear to be rotoscoping to make the bear appear to be between her and the background.
