I don't know about this specific study, but one thing about a lot of studies that link videogames to increased aggression is that they only look at aggressive tendencies immediately after a session of play. I think anyone can relate to the experience of being all hyped up after an energetic play session (why reactionaries think this is different from sports increasing aggression is a side issue.) Thing is, a short term increase in aggression due to some involving activity is perfectly normal; you do something that gets your juices flowing, then an hour later you are sitting around bored. There would only be a problem if there were a long-term increase in aggressive tendencies.