Watch the linked video: you’ll shit a brick at how quiet it is.
It’s a .45ACP carbine.
.45ACP is already subsonic, so gas moderation is relatively easy, especially for an integral suppressor. However, that round is being slowed down quite a bit to get that sound.
I’ve fired just about all the main suppressors and suppressed weapons, including the MP-5SD and the DeLisle. Rifle cartridges are another thing entirely.
Video cameras are practically useless for judging the sound pressure from a suppressed gunshot.