I'm not familiar with the original case but was the legal system ever involved for the customers?

It sounds to me like it was only Rightscorp (sidebar, what a fittingly dystopian name for a company like that) sending letters to the ISP, why would anyone be compelled to act without a court order?

Can I just start sending notifications for random IP's to their respective ISP's and hope I get lucky with one of them torrenting movies?