The railgun is lag sensitive. LPB's can use it more effectively. This works just like a high power scope on a rifle, they CAN and DO see you from a mile away and can fire that rail gun from anywhere on the board. All this without any Zbot help. So you cant tell just because he is good with the rail that he is using Zbot.
Players can snap the thing on for a second, and let the proxy take one shot, then turn it off.
You will not be able to detect a player doing this. It will not fire at dead players, or walls, or empty areas, although the player can still override and fire himself at these areas. But he cannot fire if there are legitimate targets in LOS, because the proxy will already be firing. If the proxy is active, the player cannot avoid firing at a legitimate target. Unfortunately, this looks like a player who is holding down the fire key.