And half of them are ‘below average’

Wrong, half of them are below the median.  There could just as easily be 10-90% that are below mean, it all depends on the data set.

A little refresher for mean, median, and mode:
https://www.khanacademy.org/math/cc-sixth-grade-math/cc-6th-data-statistics/mean-and-median/v/statistics-intro-mean-median-and-mode#:~:text=The%20mean%20(average)%20of%20a,Created%20by%20Sal%20Khan.