There are two separate issues here.
1) Just because something is on the internet does not mean that it is yours and that you can do anything you want with it.
It's because of the perceived anonymity and worldwide scope of the internet that people feel that they can do anything they want with it. There is tons of copyrighted material on the internet and just because you can access it doesn't make it legal for you to do anything you want with it. "Illegal" stuff goes on all the time on the internet, catching and prosecuting is the problem and for most people/companies, it's a question of effort vs. damage vs. outcome as to whether or not any action is taken.
2) Bandwidth theft. Although there are no laws on the books (that I know of) dealing with this issue, it is clearly wrong. A good analogy would be if I was able to use your cell phone connection from my cell phone, every time I get an incoming call you are charged for the minutes.
Just because you can do something, doesn't mean you should (silly concept these days, granted).
The "right" thing for this individual to have done would have been to give credit to the original creator and provide a link to his web site. (EDIT: just like what adamata posted)
