Sound is transferred through a medium literally as a wave. When you get right down to the core of it, the wave requires movement within the medium to transmit.

So it might help to conceptualize it not as “Liquid cannot move faster than the speed of sound in it’s medium” but more like “The speed of sound in a liquid medium is defined by the speed at which energy can propagate in that system, which includes motion.”

“But, when I talk to people in general, most seem to not worry because they “have nothing to hide”, and most are only worried about their passwords, banking apps and not much else.”

Sounds like they have passwords and banking apps to hide, You should demand their bank account and credit card details to verify that they have made no illicit actions.

If they point out that they have no reason to trust you with that information, that’s when you point out that police, government, or corporate groups are made out of people just like yourself. They might have some codes of conduct, or a vetting process, but it just takes one person malicious or careless enough for you to be severely impacted.