You can infer that from who the victim is and no other information. It's not exactly "was shot accidentally in a convenience store robbery".
You're right. Maybe the guy with the homemade shotgun just shot the ex-PM by accident while trying to engage in unrelated gun crimes at a public appearance of the ex-PM -- or maybe he wanted to shoot him for non-political reasons (scorned lover?). We can't know for sure that this was a targeted political assassination attempt.
> Police say the suspect told investigators that he was dissatisfied with the former prime minister and intended to kill him.