I thought it was a spray, and that was the point that he was making that one need not have a gun to stop a bear.
The caption:
Tom S. Smith, associate professor in the plant and wildlife sciences department at BYU, holds up a temporarily knocked-out family of polar bears. A study he co-authored shows that a small can of bear spray can stop a charging animal.While the spray is mentioned in regard to his study, I don't read it that he knocked out the bears with it. As far as I can tell, bear spray is just industrial-strength pepper spray. The spray will (hopefully) drive them away, but it wouldn't be able to knock them out.