There is certainly bias, however it is worth pointing out that the cited research is not rejecting the null hypothesis. Issues around sample size, methodology and study design are much more serious when a study claims to reject the null hypothesis where the burden of proof is considerably high. Furthermore, it was an almost universally accepted truth in the 90's that violent video games would lead to the total collapse of civil society (a claim that was asserted with no real evidence). The fact that a large number of people grew up with violent video games as children and now lead totally peaceful lives means that the result of this study is really not that shocking in light of people's priors.