Yes but I also think that in some cultures people sing more and informally. ot just education but also general attitudes towards singing.
For me growing up the only time I would sing would be in church - the essence of drudgery.
Working and traveling in Asia - I was exposed to people singing pubicaly a lot more. In Korea it seemed pretty common in parties or general gatherings for people just to sing. And NorReBangs (karaoke) as a common destination.
This was so foreign to me as an American. It was hard for me - fun but awkward.
Traveling in Mongolia, I stopped in gers and people would stand around and sing and ask me to sing.
This doesnt make people from these countries automatially better musicians - but I think in my particular upbringing it was really uncommon for people to casually sing. 'If you were not good at it you shouldnt do it' - was the fallacy that I internalized.
I remember my wife, when we were dating, and I were walking through a bohemian area of Seoul full of street musicians, etc and she spontaneously got up in a little outdoor ampitheatre and sang a song she liked. I thought this was great but was so outside my reference...
Japan - despite its proximity to Korea - is a pretty different culture in many ways but I felt the writer was also talking about a comfort or naturalness with music which was not the result of education but culture.