That has to be his imagination, or else maybe he's hearing some other artifact that he's mistaking for a collision between fingernail and plastic. There's no way in hell he is actually hearing what he thinks he's hearing.
Not necessarily. With good quality recording and speakers it's easy to hear things like a finger hitting a guitar string just before the string moves, lips touching a microphone, etc. I started noticing these things years ago when I first bought Blue Note recordings.
One common problem with "headphone producers" is that they often spend too much time "cleaning" audio tracks and worrying about audio leaks.
In older recordings those things were masked by other instruments, sometimes even by the room's reverb or analog noise floor, or sometimes engineers just wouldn't care about soloing tracks as much because they were on the clock and studios were expensive as heck.
Now we have everyone with super low-noise digital recording, great headphones and unlimited (home) studio time. So people spend hours obsessing about things that weren't an issue before.
What makes you so confident that is the case? I listen to lots of classical music and certainly hear musicians breathing, even on older recordings. I would imagine fingernails on a keyboard are of a similar decibel level.
