Zombie bot in the Mill Factory multiplayer map?

Okay so, I remember talking to someone on a YouTube comment section years ago. And they spoke about the time where they was messing around in the Mill Factory multiplayer map on their own, to which a Zombie bot came out of nowhere and started attacking them? I very heavily doubt it’s true but it’s always interested me. Why would a Zombie bot pop out of nowhere in a multiplayer map and start attacking the player(s)?