From my experience, and not killing bosses, I still get raids from just building. Ive had Restless Forrest, Greydwarfs - Trolls, Swamp Smell and Wolf hunt on me.

What I found was its location, location, location. I was building close to all those Biomes and had gone into them to collect different materials.

As for AllOutWar76 case, you must have buildt close to a Drauger Village in the Meadows to get that kind of raid. Thats my guess.