I believe that the commenter you responded to is referring to the fact that a quartz resonator is literally a small piece of quartz which mechanically vibrates

I believe that the commenter you responded to is referring to the fact that a quartz resonator is literally a small piece of quartz which mechanically vibrates at a specific frequency: https://en.wikipedia.org/wiki/Crystal_oscillator https://en.wikipedia.org/wiki/Crystal_oscillator