Copyright is the law from which licenses get their power. It's because the author has the exclusive rights granted by copyright protection that they can dictate the terms under which others may use their work (that is, offer licenses). When no license is offered, the author retains exclusive rights. The parent comment was implying that the author may have offered some kind of license (for example, by uploading his artwork to Flickr and ticking off one of the Creative Commons boxes in the license selection).
It's also quite possible that someone unauthorized put the picture on a site with a permissive license. That's an easy explanation for how this came about. I really do doubt that Disney or anyone representing them intended to steal this image.
