People didn’t move just because they pushed each other; there were invisible relationships causing this. By choosing to link their position to someone else, people were forced to move in response to them, and the people forcing those people to move too.
This simple action caused a new thing to happen – A whole group of moving people! We call this an emergent behaviour; that’s a group of simple nodes, like people, animals, or objects together making something more complex happen that wasn’t planned or expected.
Optional Extension
If you want to take this further, play again with a new rule added. Now choose someone to stay within two meters of too. The emergent behaviours will become even stranger. By having to keep close to some people and far away from others, you could reach a point where some of you can’t follow all the rules at once and the game falls apart. This is a “system collapse”