Except here in the UK he has broken the computer misuse act and could face jail time if someone decided to prosecute so he technically did something "malicious".
Well yes, he did break the law of course there is no denying that. But in the spirit of what he did he wasn't malicious in that he kicked off a DDoS with these printers or anything more than that, it was of course illegal but at least those people now know. One of the few internet connected devices that is actually capable of giving some output to inform the owner that something is wrong!