Hacking, IMHO is finding something cool about a thing & then taking that something and mixing it up. Make the thing do something never intended. In this particular case a kid found that he could print to printers which were connected to the Internet and then decided to start printing to printers using what amounts to a script. This isn't hacking. It's not novel. People connect printers to the Internet and he abused those connections. This is therefore a prank, not a hack.