Is that based on "average" vision of 20/20? Because apparently 20/20 is not average. It's just a baseline considered good enough. The majority of humans see better than 20/20.

This appears to be based on 20/20 (6/6) vision. People can have a visual acuity significantly better than that:

> Healthy young observers may have a binocular acuity superior to 6/6; the limit of acuity in the unaided human eye is around 6/3–6/2.4 (20/10–20/8)

> The significance of the 6/6 standard can best be thought of as the lower limit of normal or as a screening cutoff. When used as a screening test, subjects that reach this level need no further investigation, even though the average visual acuity with a healthy visual system is typically better.

https://en.wikipedia.org/wiki/Visual_acuity

I myself have been tested (twice) at around 20/8 (and was still better than 20/20 when I was complaining of blurry vision after an eye injury).