I thought so.
I feel that if 'Tabby's star' was actually being blocked by a structure big enough to do so, we would have seen/detected radio waves, electromagnetic pulses, that sort of thing
Maybe. But it can be hard to know how to look for something without actually knowing what it looks like. We don't have any examples of civilizations much more advanced than our own, so how should we know what they typically look like? I see Boyajian saying "whatever is passing between us and the star is not opaque, as would be expected from a planet or alien megastructure", and I think, who says an alien megastructure would be opaque? What proportion of the alien megastructures you've seen were opaque? (Though the scientists can be expected to exercise caution, whereas the mainstream press has tended to characterize the scientific conclusion as "definitely not an alien megastructure".)