I don't use any twitch integration mods but basically what was identical about my experience and this video was that randomly without really any causation or warning, a large horde of zombies would just come into existance which kinda sucked. its happened before too. like for example, 2 years ago i had played with one of my friends and for some reason when i was in the server a whole load of zombies would just spawn in out of nowhere. (also a note to make was that im pretty sure everytime that happened i was alone looting or something else)