As people in the other thread on this mentioned, ICE is tasked with counterfeit items, and apparently they are classifying copyright infringement in with that (notice that a lot of the domains seized look like they are for selling counterfeit jerseys, etc). So while ICE is part of Homeland Security they aren't solely concerned with finding terrorists.
That's interesting: a group tasked with protecting corporate economic interests that shares the broad powers, not to say the lack of proper oversight, of a group that's tasked with protecting the lives of people against terrorist threats. :-/