I am assuming in both of the US instances, the bears were dispatched by the game branch & they would would use rifles or 12 bores with slugs.
On the other hand, it is possible both bears were killed by the hunters.

If this was the case in BC, those bears, if killed by the hunter, had better have been killed with either arrows, or bullets from a shotgun or rifle - AND the sign (tracks) will have to show a definite charge/attack was made and the bear died within spitting distance of the hunters - otherwise, killing them would be deemed as not necessary & charges would be laid. The bear must be given EVERY opportunity to stop it's charge - before it was shot. Thus the 3 S's apply.

12 bore with slugs is what the park ranges use in Alberta. They found buckshot does not work well in griz.(we fond it is poor on big black bears as well), but a 1oz. hollow based foster slug will find the spine from a chest shot on a standing grizzly bear.
Side shoulder/rib shots are also easy kill shots with slugs. There are better slugs, though, like the Italian Gualandi slugs. Those shoot very well in my rifled Mossberg.