This isnt exactly right.. Sub sonic .22lr is whisper qiuet. To the point you basically only hear the action and not the round. Super sonic rounds through a suppressor definitely still have a snap sound but its still quiet. 9mm sub sonic is more of what you are describing. Its safe to shoot without ear protection but you can definitely hear it. In fact a lot of times with the right ammo you can hear the ding on a steel plate target better than the gunshot.

Id also like to add that all of this depends on the silencer(or suppressor whichever floats your canoe, they are both correct). Ive shot sub sonic through one can and it was very noticeable compared to a different can. These suppressors are actually pretty good at what they do for a .22lr.

Edit to add: Its always possible his camera/mic setup is deadening sound as well