yep, thats a kick I can more are less imagine doing. Here you see a forcefull downkick that acts the same way as a 2BK downkick only done with the back side of the leg instead of the frontside.
Downside seems to be a large downward push from arm and leg at the same time what gives a lot of updown movement next to the rotation.
Its the same lift and fall that can be seem with a lot of 2BK swimmers with too much pulse force in their stroke instead of smooth force.
The guy doesnt look very streamlined. If this isnt a power stroke I dont know what is.
Only for strongman, swimming this way. He is doing it with great rhythm. Can imagine this stroke feels good and powerfull if you have the strenght to keep it going.
I gues the kicktiming setlles with time. Sometimes some kicks fall in place when starting out with a relative fast kick instead of trying to swim in slow motion and consciously thinking about the timing.
Like you said, it happens more when concentrating on armtiming and rotatiing the hips and torso following the recovering arm and pushing with the other arm
No idea what legkick (s) helped rotation.
Anyway I dont think its the same basic (rotational) timing as freestyle although it may look the same.
Some good stuff on underwater dolphin kick that also applies to normal kicking I think