So snake charmer does not require killing bad guys to spawn?

I joined a "Boggy Waters" game without knowing about this and I guess the rest of the players in it is not aware either that we had started clearing the map of bad guys but never saw the Snake Charmer spawned. I found out the day after that you could actually farm Boggy Waters boss without having to kill any bad guys pretty much like how you did it in Nuris Madness before the changed in mechanics. I assumed this is a bug after they changed the rules in Nuris Madness.

Yes, his map is fully rushable; no need to kill any mobs for him to spawn. It's been this way since the launch, I believe.