The definition of Cast speaks nothing to the mechanics involved in how one actually throws a object. IMO only the "extending and drop is simply the top hand reaching back for more and bottom hand going along with it. . Although I guess one could see it as more leveling (Aiming).
The difference between what Blackmon is doing with his wrist vs the posters DD, is that Blackmon is actually acting on the bat handle vs the posters DD hand just rotates/slips around the handle of the bat, with the top hand independent of the bottom hand. Both the top and bottom hand of Blackmon actually apply force in unison on the bat handle. Posters DD does not. Again look at the following gif. Notice the blue stripe on the top hand batting glove moves independent of the bottom hand with is competely stationary and compare to blackmon that you posted. I personally believe that's because blackmon know how to have active hands especially the bottom hand
maybe bc the lead shoulder is dead? Or not loaded? Leveraged? It’s a chain of movements CL. The bottom hand pulling is ok. But it must be done w the slack out. Does the young lady take the slack out when Blackmon does? Why not?
edit: looking at one piece can/is misleading. Cause and effect is the swing.