I don't think an otherwise normal, well-adjusted individual is going to turn into a homicidal maniac just after playing a video game. So if that's what they mean when they say "no connection between video game violence and violence in society," then I would agree. But it may be a combination of factors.
It might also have to do with the amount of attention these mass shootings generate. The media make these mass murderers into instant celebrities who will be remembered for decades.