22 Hornet is a pretty popular cartridge to shoot treed lions with.
You can not compare a single projectile fired from a .22 Hornet, or even a .22 long rifle, to birdshot. The hunter in the article was bird hunting, he fired two rounds, birdshot I presume, into a cougar at ten yards, and the cat expired soon there after.
I am curious to what loads he was using. Maybe some grouse hunter out there could help speculate on that.