My personal theory (not having been able to ride the boolit like our lovely mascot all the way to and through the deer) that it's a combination of Boolit expansion, speed, boolit design, and the intended target.
You can shoot a HP boolit and get an energy dump, you can shoot a FN boolit and get a shockwave, or you can shoot a 300 winmag with a super hard jacketed bullet and get penetration, but when you quit trying to make just one of these your sole focus, and instead learn to balance them so that they play off one another, magic things happen.
The boolit impacts the game at saucy speed and the FN sets up a shockwave, and the nose of the boolit deforms, following the damage and making it greater rather than penciling past it. It popps out the other side of the game at 1/10 the speed that it hit with, and twice the diameter, because it gave all it had.
When you can get the boolit expansion to follow the shockwave, and have just enough speed to keep the boolit in that place, then you get what you see in the OP. I think there are "sweet spots", or combinations that do this, and it applies to jacketed as well as cast, and it occurs all over the speed spectrum.
I know guys that have absolutely killer combos that use a 45 caliber boolit at subsonic speeds. These loads have more effect than another load that is faster.
Why do you think there is such a stark difference between 45-70 performance and 444marlin? Many would say that the .444 has superior effect.
Why does a .270 Winchester generally have better effect on deer than 7mm magnum or 300 Winchester magnum? There is very little difference the speed, and only slight difference in bullet style and design, and yet, the results speak for themselves (albeit blood shot meat is not the results that we are particularly looking for here).
When I say that the cast lead boolit is the most effective projectile in the world, I mean that tit for tat, its ability to have an effect on game is much greater than jacketed projectiles are able to, for good or for bad.