This is like in times past a people believing that they could detect any other intelligence by seeing the smokes from their fires. After all how else would they

This is like in times past a people believing that they could detect any other intelligence by seeing the smokes from their fires. After all how else would they cook their food or create light to see in the dark? A dyson sphere isn't some profound insight into the universe. It's a relatively straight forward idea once we achieve the understanding that we can capture EM energy and convert it into other usable forms of energy. Of course before that revolutionary discovery or EM utilization it's something that would seem completely nonsensical.