I think we judge smartness in relation to ourselves. Of course dolphins can't make tools and can't operate heavy machinery and so forth, but they do exhibit behavior much like humans. This is why we deem dolphins smart, well at least smarter than other animals. They can communicate with one another and also with us. These behaviors show a sort of evolution or gravitation towards intellect. They won't be doing advanced Calculus anytime soon but that's because their environment dictates this. We have expanded ourselves to almost every reach of the earth and therefore require lodging. We started building homes and after a while we built bigger homes and after a while more built large buildings and skyscrapers. Throughout all this we've advanced our intellect, our smartness to accomodate our needs. Dolphins number 1 priority in the "wild" is to survive. So there is only a certain degree of smartness that they can reach. I don't think dolphins are dumb. But I also don't think they are smarter than us.