I'm a little confused by part of this article. The author states part of the evidence they used for deciding something was wrong is that a search not restricted

I'm a little confused by part of this article. The author states part of the evidence they used for deciding something was wrong is that a search not restricted to Creative Commons licensed images included many images with open source licenses and some in the public domain. If you restrict your search to Creative Commons licensed images why would you expect images under other open source licenses or in the public domain to be returned?