Seriously there is no invasion for them to defend against; the Boston bombs make them look stupid; money is tight; perhaps this is all they have to avoid being fired for uselessness?
This could be a possibility. Government always tends to go for a reward-by-result numbers game. I wouldn't be able to say such a thing is true, because I'm not in a position to say just how much impact the DHS really has on the activity of terrorists. I think in the end though a strategy such as this would be moot, as you would be chasing phantom cases. "We thought this was the action of terrorists but wasn't, oops" might be a lot worse than "we have thus far found no sign of terrorist threat." Having one rather small article to go on makes assessment of exactly what the DHS is doing in this case is all but impossible.
The tone of the OP's article says "Look at me - I am not a waste of money." It's not a huge issue that DHS got used instead of the local cops to arrest hucksters selling fake copyrights. But it is interesting that they have so little work that is what they are told to do.