When hunting with a handgun or a rifle, jacketed bullets or cast, there's just no set rule on how the bullet will work or how the animal will react. Thats one of the reasons we can't draw conclusions from one or two examples.
Probably the most pathetic thing I've ever seen while hunting was a pronghorn antelope that a guy had shot with a 7mm magnum, it was literally shot to pieces & had run perhaps a mile before laying down & he gave it a finisher.
Sometimes a bullet will deflect on bone & run right down the a leg or maybe along the neck, doesn't usually happen with cast slugs but it has happened. If you stay in this hunting game for very many years you're going to see some things that you just can't explain.
Until I see it with my own eyes I'll stick with heavy for caliber cast slugs at 1100-1200 fps, cast from an alloy that gives me good accuracy, again, I don't worry about expansion, I want bullet placement & comeplete penetration.

Dick