I'd wager it's a tear gas canister Seems more likely to enrage a bear, while a flashbang would just confuse and daze a bear (in my uneducated opinion)
Honestly both would probably have very disorienting effects on a bear. A flash bang in a confined area is going to fuck up a bear's ears, perhaps permanently, and probably effect its equilibrium. So now it's blind and deaf and staggering drunk. Tear gas on the other hand is going to probably have a similar effect to bear spray, although they have different compounds. Odds are that bear is going to be terrified more than hostile in either scenario.
