this artsi is talking about power. saying that being powerful can turn someone and make them step on other people thinking that they are above and not equal. as you can see he is blocking the water by squeezing the pipe and not letting the kid have any.
Didn't read the article, but I really like the picture. A great reminder, not just that we are to be kind to everyone, but also that anyone, no matter how small, can make a different for the kingdome through a simple act of kindness. Banksy's street art: 25 Ways to Be Good for Someone Else