I think you could summarize this article as "Gamer dislikes griefers, thinks gaming is serious business". It sounds like it was partially on the game designers to limit this griefing activity and make this character able to be killed. The professor's purpose was to study this community and in doing so he put it under stress and watched it react. I think this is valid research given that no one was actually hurt-just annoyed.
It seems like this guy should be more upset with the developers who did nothing (that's cited in the article) to stop this.
It may be a valid and interesting result, but I don't think it was ethically collected. I'd love to hear how these human subjects were briefed or compensated for this study. It's pretty clear the professor was subjecting them to unexpected emotional stress without their consent.
It may also be valid and interesting to find out what happens if you flip people off in traffic, or pay for your restaurant bill in pennies, or taunt preschoolers when you beat them in a game, but it doesn't mean it's ethical to just go out and do it, even if there's nothing explicitly saying it's illegal.
It seems like this guy should be more upset with the developers who did nothing (that's cited in the article) to stop this.