The first arrow hit low and back in the guts.

This arrow (broadhead and some shaft) is seen protruding from the bear's left side after the second shot and the bear comes up higher on the slope. The broadhead, dripping blood, is protruding out the bear's guts. After the bear is dropped, there is a closeup of the bear on it's right side and a bunch of bloody fat sticking out the gut exit hole.
The second shot was a good one and was very well placed.

The first, all important shot with a bow (or any firearm on a bear), was simply a very poor hit.