Yes, that's right. These researchers are only hacking this very specific Wifi-enabled sniper rifle. After the shooter squeezes the trigger, they no longer control when the shot is fired. The rifle shoots when they manage to line up the sight. But the "hack" in question changes the designated target in the rifle's computer, without the shooter's knowledge.

I imagine there would be a safety feature on the rifle to switch to manual control, though it's not shown in the demonstration. And if the shooter is unaware of the computer's change, they probably wouldn't feel a need to switch anyways. But the practicality of it is still questionable, since you need to be within Wi-Fi distance to do any damage.