This is normally inside a web contract, it's pretty easy to write a sentence saying "all media content will have the appropriate license and usage rights yadda yadda...", this isn't even due diligence, it's common. It's the job of the web developer to educate a client, in the case of a copyright infringement company you would think the operators have more knowledge of thier assets unless they were flat out lied too.

For a company that specializes in copyright infringement I find their stance unacceptable, how can you possible trust their business process if they are making mistakes which they supposedly enforce..

It's important to note they are also using copyright javascript that has proper attribution in the source, though it is not following the exact rules ( you could nitpick that it's not in the header as requested).