When your making a script how would it tell the difference from a zombie nps and a player?

you would either check if there's a player instance with the same name as the NPC, or use the method, Players:GetPlayerFromCharacter(character) which will return a player object associated with the character passed to it, or nil if the character passed to it is not a player's character..

i recommend using the second method, because maybe in an extremely rare case there might a be player who is named the same thing as an NPC, therefore giving you wrong results.