The 3 cubs were in good shape and couldn’t be trapped. In addition, there is yet another sow with 3 cubs in the area!
Rather than some marginal glade far from grizzly country (the Eldorado Grove), this sounds like grizzly central at this time of year where the bears are fat and cubs do well.
Here is a followup story in the Choteau Acantha. Pheasant hunter shoots grizzly sow