Usually these companies attack uploaders (even if just due to regular p2p seeding) or, as in this case, people who run systems that "facilitate" infringement. The claim is not based on what you should have paid, but on all the money that the people who got a copy from you would have paid.

In a fair system they'd have to prove those damages, but alas, copyright laws often include "statutory damage" provisions to help them avoid that requirement.