If I understand this question correctly, you are asking if there is some other way to explain the greater degree of violence among adults who watched a lot of TV as kids. If so, there are at least two things to consider.
First, there is the possibility that there is something about people who are prone to violence and aggression that draws them to watching TV. In such a case, the TV watching would not be causing the violence. Instead, the violence and the TV watching would both be the effects of some personality trait.
Second, there is the possibility that the people who watched a lot of TV were different in some other way as well. It could be that people who watched a lot of TV had less interaction with their parents. Or it could be that they came from poorer households that placed less emphasis on education. In these cases, it could be that the other variable (parental attention, emphasis on education) is what really causes the violent behaviors in adults. It is very hard for researchers to control for these sorts of factors when doing studies of TV and aggression.