I saw it too but being it came from the Turner Broadcast Company they probably did intend it as a terror like joke. It was funny watching CNN report of the terrorist hoax not knowing it would turn out to be their own parent company.
Adult Swim is a tiny subsidiary of Cartoon Network which is a tiny subsidiary of Turner Broadcasting...
I know people love the mental image of an evil Ted Turner rubbing his hands dreaming up marketing schemes where he plants hoax terrorist bombs but the reality is I doubt Turner has even heard of the show and I'm fairly sure he didn't have the foggiest idea about the marketing scheme.
The only real bombs made by Turner Broadcast Company are their shows ;-)