It's an open world game, but let's assume you mean local map.

In that case, let's assume that each player waves (/wave). I've done this before with >50 players and took a screenshot and we were all in sync. It's also possible to have 50 players in the same area fighting in real time, e.g., in a battleground. This was back in 2010 when I played ... So I am not sure if it's any fabrication at all, otherwise everyone would die, etc? Given players have health, take damage, get healed, etc.