That is true! Lead in the bear spray was in common usage during the Lewis and Clark expedition.
It would be interesting to know the breed of dog(s) the hikers had with them, even though it likely would have made little difference in the end. I suspect that if people viewed black bears as 2, 3, 400+ pound Rottweilers capable of moving 30 mph (which is essentially what they are), they would not pin their hopes on a can of pepper spray.