They pull it right out of their asses

I prefer to do these metrics based on 21 million divided by 4 Billion (estimate of actual economic actors, so children and elderly excluded)

If Bitcoin was perfectly evenly distributed, everyone would have about 525,000 sats

You can apply whatever curve you want to this and fit it for your own personal results

Obviously most people aren’t holders now so most are stuck on zero, but the long term question of wealth distribution is about future holders, not current ones