Thanks for explaining. I think I understand a little better now.

This Wired article also helps,

  Coulton said that while his lawyers have been looking
  into the copyright issue, it seems unlikely that he
  will have any legal recourse. ”It seems that because of
  the compulsory license I purchased when I made a cover
  of this song, the arrangement itself is not protected
  under copyright, although it’s the darkest gray of the
  gray areas [of the law]… While there may be some weird
  offshoot of the law, it doesn’t seem like something
  where a little guy could sue to get any satisfaction.”

http://www.wired.com/underwire/2013/01/jonathan-coulton-glee...