I don't think it was communicating with anything. We were broadcasting to whomever would listen and Rorschach was moving through space listening for prey. My metaphor for this was a shark- Rorschach and its ilk just coast through space until someone's dumb enough to say "Hey, we're intelligent and have resources!", at which point Rorschach flies over and kills them. It will react the same way to anything trying to communicate- the ability to communicate is threatening to Rorschach. Similarly, as we've demonstrated with Voyager and similar probes, we'll gab away with anyone who's willing to listen. We have no sense of how dangerous space is.