Rightscorp can't claim the subscriber is actually infringing their customers copyright, as their software tool can simply see if the information is available from the host in question but it cannot tell anything else about it. They have no way to know that anyone other than their self has actually downloaded the information in question. They can only guess and I hate to say it but you can't sue over speculation.
54,000 claimed infringements over 64 days sounds like a lot, but it's basically just under once per second, and claiming each time is another incident of infringement. So basically their software is constantly checking the ip, and this could be argued constitutes theft of service since both Cox and the customer in question pays for the bandwidth.
As for them downloading the information themselves, since the tool and the company that runs it is authorized by the copyright holder to search for and access their copyrighted files one could easily argue that no actual infringement taking place.
I also think Cox should establish a reasonable handling charge for investigating and dealing with these automated complaints, I think 10$ per complaint sounds about right. So 54,000 x $10 = $540,000. Plus attorney fees and costs for this frivolous lawsuit.