If the story being reported is true it sounds like he was an apolitical kid raised in maga who began seeing the wrongs of maga and leaning antifascist. If so it's likely that maga primed him to do violence but antifascism gave him the trigger and the target.

That tracks given how basically every major political shooter or mass shooter with any background on the left also had a right wing background, with the arguable on every point exception of Luigi (may not have done it, may not be considered left, his ties to the right can be questioned)