As part of the devs farewell message on their site, they have included malicious code to make each visitor sends 2,000 requests to the dbzer0 servers in an attempt to DDOS and take the instance offline.
That's roughly what I remember: the threats were against "zionists" or "genociders" or similar, not any particular user by name, but this guy basically told on himself by interpreting it personally anyway.
(It's possible I'm unaware of other, more egregious, behavior as the situation escalated, but I think this was at least the thing that started the pearl-clutching initially.)