What the study fails to test if the depression is the cause of the video game playing.Greg Tito said:Snip
The study didn't indicate if say the children in question are be socially rejected (and are now depressed) and have turned to their hobby to escape the real world.
It would be like seeing that the teenagers that are not in school drink the most coffee, then concluding that coffee kills braincells and makes kids go out of school. What is equally likely that is happening is that teenagers that dropped out just have the time to drink more coffee.