I love how the "80/20" rule gets stretched so often that in this article it talks about hyperdominate trees that take up 50% of the Amazon. So 80/20 can go anywhere form 99/1 to 50/50. What an interesting "pattern"
You're reading the numbers wrong, there is no stretching. The 80/20 rule means that 80% of resources is controlled by 20% of participants. Applying the same ratio to subgroups, you also get that 1% of participants control about 50% of the resources, as for trees in Amazon. The 80/20 number is just nice and commonly used because it adds up to 100.
It is an example of accumulative advantage, which the article author claims underpin the 80/20 rule.