Somebody who played the game very early could answer this, but I'm assuming that's the original PVP mode that sucked and prompted them to outsource a PVP mode, which resulted in Battle Royale.
I'm not sure this even made into Online Tests, I don't remember it in OT3, but it wasn't in later ones for sure. However for a while in later OTs there was a leftover of that mode - there was a way to indirectly cause another player to die and you would get a screen from that PvP mode along the lines "you were eliminated by player X". There's a chance you can find this in the early OT videos for Fortnite that are still there on the YT channel.