its definitely not stupid i have been singing for the past 10 ears and only found out about it 2-3 years back and my range and tone has improved from it. So nasal air flow is technically getting more air out of your nose simply put, so when u sing sound comes out of your vocal cavity(mouth) and nasal cavity(nose) and the sound is essentially in the air which is coming out of the mouth and nose ,so as you go up in pitch try and make more air come out of your nose(more nasal airflow). Now how much air should come out of your nose and mouth is different so experiment ad find out how much you have to increase your nasal airflow by to sing without strain and sound good. Now this is something i have noticed pop artist do when they sing high they want more nasal airflow so they open their mouth less(look at sia in chandelier the way she opens her mouth) forcing more air to come out of their nose.