Putting aside their qualifier "may" - desensitisation doesn't necessarily mean someone is more likely to run out and kill people, although I'm sure some anti-game proponents will immediately jump on that particular fact.
The article also doesn't mention exactly when they played these games - did they play it early in the day, or right before they went to sleep? Because that makes a major difference. Just sitting in front of a PC browsing the web or watching videos can already have a negative effect on sleeping patterns; games that contain a lot of action and require concentration elevate this effect quite drastically - the brain requires some time to drop out of the activity high.
And following that, disturbed sleeping patterns naturally lead to elevated stress-levels and exhaustion. It's kind of a chicken and egg question, to be honest.
