The 80-90% claim seems to be repeated in various areas on the internet, including by the American Academy of Ophthalmology, which I assume to be reputable:

Over recent decades, the prevalence of myopia has skyrocketed, particularly in Asia. In countries like China, Japan, Singapore, South Korea, and Japan, up to 80-90% of teenagers and young adults are now myopic.

Of course these local averages are still consistent with a lower global average