Found the altar to N'Kuhana... Without finding it

I had seen the achievement in the logbook, had no idea where to find the altar, but I'm 3h into a run, blowing the whole map up in the wetlands when all of a sudden I get the achievement... I was confused as hell, ran around for 10 minutes looking for the thing before looking it up on the wiki and heading into the secret area to have a look. I guess I had enough AoE to kill the skeleton through the map?