How can someone hear the diastolic pressure?

You don't: When we take the blood pressure, we blow up the cuff and then slowly let it deflate. When one hears sounds, that is the systolic pressure. When the sounds stop, or become very muffled, that is the diastolic pressure. So you hear nothing.

You don't: Actually the diastolic blood pressure is the point at which you no longer here a tapping sound as you slowly release the pressure in the blood pressure cuff. So it is actually not hearing the sounds. Sometimes instead of disappearing completely, the sounds just get muffled at the level of the diastolic pressure.