In short, as put by Epic Games founder and CEO Tim Sweeney in a social media post, "It’s Discord bots going bad." Though, the full answer is a bit more detailed.
As for the decidedly less important statistics Bungie shared from the Server Slam, it's clear that things got pretty hairy on Tau Ceti. Out of 16,554,683 deaths, 9,152,844 of them were caused by other ...