If violent video games made people violent, 100% of players would become violent after playing violent video games.
What MattPat suggests in the video just makes sense, and i'm sure the same could be found for violent films, music genres, books etc which have been blamed for atrocities and crime previously. People predisposed to violent actions are more likely to seek out that kind of scenario.
The next video proves to be an interesting one, though: Can violent games make people LESS likely to be violent by making them MORE sociable?
Look at Australia: Bought in gun restrictions in 1995 but have not had a mass shooting atrocity since - computer game censorship is notorious for that country but if you look at the list of games banned, you won't find some of the most notorous mass-shooting scenes in video game history, like the COD level where you play as a terrorist gunning down an airport full of travelers. You'd expect Australia to have had more violent gun crime as only the criminals have guns and tehy allow violent video games which cause violent behavior, but it doesn't seem to be that way.
I look forward to the findings.