Correct. Disrupts shock wave to deaden the sound. Bingo.
I was underwater a few times when I fired my 40 cal, I wore ear plugs first, then took them out- the water seemed to absorb the blast way more effectively than any suppressor I ever used. In the air, it seems like the blast is a whole lot of gas- under water- a medium sized balloons’ worth of a bubble- Discharging 34k psi of powder gas under more than atmospheric pressure attenuates it quite well.
The tube they show has holes along its length- a suppressor as we know it, it is not!