It doesn’t matter what type of music a musician plays, whether it is rock, jazz, bluegrass, or country music. Even if they have learned to play music by reading music, they have still listened to music and plucked it out on their instrument.
Hey, I am an accomplished piano player who plays the piano (keyboard, for you modern listeners). And, even though my mother handed me a program to learn how to play by ear, written by an accomplished professor of music and a college known for their music program, it was not the zing that put the learning in my soul. Instead, it was getting down to business and simply tinkering with the piano and playing what I heard. There was really no “program” that did it. Instead, doing it did it! Does that make sense?