The problem with these kinds of studies is that the methodology is typically either flawed or garbage. In order to establish a causal relationship, you have to be able to ratcheted down every variable except the one your testing for.
So all these kids play violent video games. Do they also watch violent movies? Television? What are their dietary habits? How much exercise are they getting? What are their parents like?
It is entirely possible that the video games are the culprit (I highly doubt it, but it is possible). However unless you can rule out every other possible cause, you can't say with any certainty that this is it.
Since the article talks about the study but offers only vague details about the methodology, it's impossible to tell if the research is even remotely valid. It sounds as though you're pretty skeptical of their findings as well