Because what you did, carving with your sword was not allowed. No matter how bored you are, you are not allowed to do that. So you were asked to do the painting. If you hadn't done that, there was no need for you to paint anything.

Hikaru and Kaoru at the moment are in no position to punish outsiders. But trust me... [He shudders.] You don't want to know what goes on in their minds.